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Full text of "IES lighting handbook: the standard lighting guide"

UNIVERSITY 
OF FLORIDA 
LIBRARIES 




Digitized by the Internet Archive 

in 2011 with funding from 

LYRASIS Members and Sloan Foundation 



http://www.archive.org/details/ieslightinghandbOOinillu 



IES 
LIGHTING HANDBOOK 



Current Publications of the 
Illuminating Engineering Society include 

ILLUMINATING ENGINEERING 

(a monthly journal) 

CURRENT PRACTICES 

American Standard Practice of School Lighting 

Recommended Practice of Office Lighting 

Lighting Practices for Stores and Other Merchandising Areas 

Recommended Practice of Home Lighting 

American Recommended Practice of Industrial Lighting 

Ameriean Standard Practice of Street and Highway Lighting 

Lamps for Aerodrome and Airway Lighting 

Recommended Practice for Laboratory Testing of Fluorescent Lamps 

LIGHTING DATA SHEETS 

(Photographs, plans, and detailed information on actual installations) 

REPORTS 

Standard Method for Measuring and Reporting Illumination 
from Artificial Sources in Building Interiors 

Art Gallery Lighting 

Lighting of Power Presses 

Lighting in the Shoe Manufacturing Industry 

Study of Table Tennis Lighting 

Lighting Performance Recommendations for Portable 
and Installed Residence Luminaires 

Brightness and Brightness Ratios 

Visibility Levels 

The Interreflection Method of Predetermining Brightnesses 
and Brightness Ratios 

Brightness Distribution in Rooms 

Illuminating Engineering, Nomenclature and Photometric Standards 

STUDY AIDS 

Experiments with Light 
Lessons in Practical Illumination 



IES LIGHTING 
HANDBOOK 

The Standard Lighting Guide 



REFERENCE DIVISION 

Fundamentals of 
Illuminating Engineering 



APPLICATION DIVISION 

Current Practice 
in Lighting 



MANUFACTURERS' DATA 

Information on Lighting 
Equipment, Supplied by the Makers 



INDEX 

A Complete Alphabetical Index 
to All Sections 






FIRST EDITION 



Published by the 

Illuminating Engineering Society 

51 MADISON AVENUE, NEW YORK 10, N. Y. 

1947 



'RE 
BOOK ROOM 



Copyright 1947 

BY THE 

ILLUMINATING ENGINEERING SOCIETY 



Reproduction of text or illustrations 

may be made only with the specific 

permission of the Society 



COMPOSED AND PRINTED 
BY 

THE WAVERLY PRESS 

Baltimore, Maryland 

1947 




PREFACE 

Through the years since 1906, the Illuminating Engineering Society has 
been publishing the findings of the leaders in the fields of lighting application 
and research. In addition to the 41 volumes of its journal, the I.E.S. Film, 
and the many lighting installation data sheets, pamphlets and books pre- 
pared under its sponsorship, there is today so much excellent literature 
on lighting published by others that it has become exceedingly difficult 
to keep abreast of advancement along the ever-expanding lighting horizon. 
For one person to collect and digest the findings of the past half-century of 
progress would require a life-time of research. Nevertheless, an under- 
standing of the basic technical information and of time-tested application 
techniques is recognized as the best foundation for further advancement. 
It is conceived by the Society that this Handbook will provide its readers 
with the essential information required in their daily work. 

In simple terms and highly condensed style the IES Lighting Handbook 
places conveniently within reach of all its readers the accumulated knowl- 
edge of the past forty-one years of lighting progress, evaluated and in- 
terpreted with respect to today's needs by a highly qualified group of over 
100 contributing specialists — engineers, architects, physicists, decorators, 
artists and opthalmologists — who have worked for more than two years 
under the direction of a special committee of the Society and a full-time 
editorial staff to provide the most complete coverage of the field possible 
within the limits of a conveniently-sized volume. 

In many ways the IES Lighting Handbook is particularly well-adapted 
to reader convenience. For example, the type face is larger than that often 
encountered in engineering handbooks and, in combination with the mat 
finish paper, is more legible. To make clear and easily understood all 
points of particular importance, an unusually large number of carefully 
selected photographs and specially prepared line drawings are included. 

The detailed alphabetical index provides a simple means of finding dis- 
cussion on subjects of interest, and the original literature referenced at 
the end of each section will amplify the condensed handbook treatment. 

To aid in completing lighting installation plans, detailed data on many 
types of commercially available lighting equipment are included in the 
Manufacturers' Data Section. 

In some instances, as in the case of the Average Brightness Calculation 
Procedure, formerly thought to be a complex tool of the mathematician, 
it has been possible, for the first time, to simplify design techniques, and 
other working tools, so that now they may be used easily by everyone. 

Every precaution has been taken to secure broad coverage of all phases 
of lighting and a completely objective approach. First, the integrated 
views of several different specialists were incorporated in each section of 
the manuscript and, finally, the printer's proof was read and approved by 
a Board of Review including the President and several Past Presidents of 
the Illuminating Engineering Society. 



We wish to acknowledge with sincere appreciation the assistance of the 
many individuals who cooperated in the preparation of the manuscript. 
The following list of names of the contributors cannot reveal the hours of 
effort which they devoted to the work. Each deserves a large portion of 
credit for the completion of a difficult assignment. 

CONTRIBUTORS 



Elliot Q. Adams 
Charles L. Amick 
William T. Anderson, Jr. 
Carlyle A. Atherton 
George R. Baumgartner 
Norman C. Beese 
Conrad Berens 
Frank Benford 
O. Howard Biggs 
Faber Birren 
Ralph R. Brady 
Arthur A. Brainerd 
Francis Breckenridge 
A. Carl Bredahl 
Lorin C. Brown 
William D. Buckingham 

LEROY J. BUTTOLPH 

Frank E. Carlson 
Donald P. Caverly 
Albert H. Clarke 
Wilfred E. Conley 
James L. Cox 
Eugene C. Crittenden 
Cazamer L. Crouch 
Herman E. D'Andrade 
Robert L. Dearborn 
Leo Dolkart 
Creston Doner 
Arthur C. Downes 
Allen J. Dusault 
Warren H. Edman 
Myrtle Fahsbender 
Ralph E. Farnham 
William E. Folsom 
James C. Forbes 
William E. Forsythe 
Kurt G. Franck 
G. William Frederick 
Allen K. Gaetjens 
Henry P. Gage 
Bernard F. Greene 
Jean F. Gschwind 
James D. Hall 
Eric B. Hallman 



Arthur C. Hardy 
Robert F. Hartenstein 
Henry H. Helmbright 
Samuel G. Hibben 
Caroline E. Horn 
John P. Hoxie 
John P. Huebsch 
Maryon J. Ingham 
Edgar W. Jeffrey 
Leon Johnson 
Loyd A. Jones 
Deane B. Judd 
William II . Kahler 
James M. Ketch 
John L. Kilpatrick 
Paul A. Kober 
George E. Korten 
John O. Kraehenbuhl 
johan c. kromhout 
Emil Kun 

Warren W. Langston 
Maurice K. Laufer 
William F. Little 
Henry L. Logan 
David L. MacAdam 
Charles T. Masterson 
Stanley McCandless 
John W. McFarlane 
Helen G. McKinlay 
O. Phelps Meaker 
Gordon G. Milne 
J. Dixon Mitchell 
John W. Mollica 
Parry H. Moon 
Wesley S. Mowry 
Frank E. Mueller 
J. Harvey Nelson 
Dorothy Nickerson 
William C. Norvell 
Brian O'Brien 
Lawrence B. Paist 
Jack F. Parsons 
Willis A. Pennow 



Miles Pennybacker 
Lawrence C. Porter 
Wentworth M. Potter 
Priscilla Presbrey 
Gwilym F. Pride aux 
Ellery H. Raddin 
Fred Rahr 
Edward V. Rambusch 
W. Clifton Randall 
Kirk M. Reid 
Harris Reinhardt 
Andrew E. Reynolds 
Val J. Roper 
Dana W. Rowten 

LlNDSLEY SCHEPMOES 

William H. Searight 
Howard M. Sharp 
George E. Shoemaker 
Richard E. Simpson 
Richard G. Slauer 
Domina E. Spencer 
Raymond J. Stefany 
J. William Steiner 
Jonathan C. Stimson 
Everett M. Strong 
Walter Sturrock 
John A. Summers 
Ray P. Teele 
Francis T. Tillemans 
Victor H. Todd 
Richard F. Townsend 
Beverly A. Travis 
Davis II . Tuck 
Dorothy Tucker 
Leslie C. Vipond 
Fred J. Vorlander, Jr. 
Charles E. Weitz 
Kenneth C. Welch 
David L. Williams 
Frederick C. Winkler 
C. Scott Woodside 
Robert R. Wylie 
Irvine A. Yost 
Robert J. Zavesky 



The part played by the IES Lighting Handbook Committee and by its 
Board of Review was most important. These men contributed their best 
thinking and experience both before and after the production of manuscript 
had begun, and during the reading of proof, in establishing the basic pol- 
icies which are revealed in the completely practical character of this first 
edition. Their critical appraisal and check of the manuscript after its prep- 
aration added much to its overall utility as well as to its technical accuracy. 

HANDBOOK COMMITTEE 

C. A. Atherton, Chairman J. L. Kilpatrick 

A. A. Brainerd H. L. Miller 

F. C. Eley J. W. Milford 
J. M. Guillory R. G. Slauer 

G. K. Hardacre, (ex officio) Walter Sturrock 
C. C. Keller, Vice Chairman H. O. Warner 

S. B. Williams 

BOARD OF REVIEW 
D. W. At water E. C. Crittenden 

Conrad Berens Ward Harrison 

L. H. Brown P. S. Millar, Chairman 

R. B. Brown, Jr. R. W. Staud 

The preparation and publication of the Handbook proceeded under the 
administration of the following Presidents of the Illuminating Engineering 
Society: 

R. B. Brown, Jr. A. F. Wakefield 

H. M. Sharp G. K. Hardacre 

S. B. Williams R. W. Staud 

The General Office Staff took an active part in many phases of the work 
under the direction of A. D. Hinckley, Handbook Business Manager and 
Executive Secretary of the Society. C. L. Crouch, the Society's Technical 
Director, acted as Handbook Editor during the formative stages of the 
project and made many investigations upon which the plans for publication 
were based. 

Recognizing that much remains to be learned about light and its applica- 
tions, we feel, nevertheless, that this first edition Anil faithfully serve its 
readers. It is inevitable in a book of this size that some errors and omis- 
sions will be discovered. Your cooperation in calling them to our attention 
will be appreciated. 

Robert W. McKinley 
editor 



CONTENTS 



Preface 

Contents 

Illustration Credits 

REFERENCE DIVISION 

Section 1 The Physics of Light Production 

Section 2 Light and Vision 

Section 3 Standards, Nomenclature, Abbreviations 

Section 4 Color 

Section 5 Measurement of Light 

Section 6 Light Sources 

Section 7 Light Control 

Section 8 Lighting Calculations 

Section 9 Daylighting 

APPLICATION DIVISION 

Section 10 Interior Lighting 

Section 11 Exterior Lighting 

Section 12 Sports Lighting 

Section 13 Transportation Lighting 

Section 14 Photographic, Reproduction, Projection and Television 

Lighting 

Section 15 Miniature Lamp Applications 

Section 16 . . . Miscellaneous Applications of Radiant Energy 

APPENDIX 

MANUFACTURERS' DATA 

INDEX 



Note: Pages are numbered consecutively within each section, 
each page number is preceded by the section number. 



ILLUSTRATION CREDITS 

We are indebted to the mar^ individuals and organizations who con- 
tributed the multitude of photographs and drawings from which those used 
in the Handbook illustrations were selected. In preparing the list of credits 
every attempt has been made to identify the source or sources of each il- 
lustration and table. However, this has not been possible in all cases. 

So many excellent photographs were contributed that only a small portion 
of the total could be included in the Handbook. The availability of the 
larger number made possible the establishment of the highest standards for 
the final selection. 



CONTRIBUTORS OF ILLUSTRATIONS AND TABLES 



1. AcmeElec. &Mfg. Co., Cuba,N.Y. 

2. Ainsworth Lighting Inc., New York 
8. American Institute of Physics, 

Journal of the Optical Society of 
America, New York, N. Y. 

4. American Society of Heating & 
Ventilating Engineers, New York 

5. Architectural Lighting Co., Chicago, 
Illinois. 

6. The Art Metal Co., Cleveland, Ohio 

7. Association of American Railroads, 
New York, N. Y. 

8. Bausch & Lomb Optical Co., 
Rochester, N. Y. 

9. Bell Telephone Laboratories, N. Y. 
10. Benjamin Electric Mfg. Company, 

Des Plaines, 111. 
It. Better Farm Buildings Assn., 

Ardsley, N. Y. 
12. Boston Edison Co., Boston, Mass. 
IS. Buffalo Niagara Electric Corp., 

Buffalo, N. Y. 
14- Civil Aeronautics Administration, 

Dept. of Commerce, Wash., D. C. 

15. Connecticut Light & Power Co., 
Waterbury, Conn. 

16. Consolidated Gas Electric Light & 
Power Co. of Baltimore, Balto. Md. 

17. Consumers Power Co., Jackson, 
Michigan. 

18. Corning Glass Works, Corning, 
New York . 

19. Grouse-Hinds Co., Syracuse, N. Y. 

20. Curtis Lighting Inc., Chicago, 111. 

21. Cutler Light Mfg. Co., Phila. Pa. 

22. DayBrite Lighting Inc., St. Louis, 
Missouri. 

23. Department of Water & Power, 
City of Los Angeles, Calif. 

24. Detroit Edison Co., Detroit, Mich. 

25. Detroit Steel Products Co., Detroit, 
Michigan. 

26. R. E. Dietz Co., Syracuse, N. Y. 

27. Duquesne Light Co., Pittsburgh, Pa. 

28. Eastman Kodak Co., Rochester, 
New York. 



29. Eastern Airlines Inc., New York 

50. Electrical Construction & Main- 
tenance, New York, N. Y. 

51. Electrical Products Inc., Seattle, 
Washington. 

32. Electrical Testing Laboratories 
Inc., New York, N. Y. 

33. Electrical World, New York, N. Y. 
34- Fluorescent Lighting Assn., New 

York,N.Y. 

35. Fostoria Pressed Steel Corp., 
Fostoria, Ohio 

36. Franklin & Charles, Lancaster, Pa., 
General Physics, Franklin & Gran- 
tham . 

37. Frink Corporation, L. I. C, N. Y. 

38. General Electric Co., Cleveland, 
Ohio, Schenectady, N. Y. 

39. General Luminescent Corp., Chi- 
cago, 111. 

40. General Outdoor Advertising Co., 
Chicago, 111. 

41. B. F. Greene, Illuminating Engi- 
neer, New York, N. Y. 

42. Greenway Reflector Mfg. Co., 
Philadelphia, Pa. 

43. Edwin F. Guth Co., St. Louis, Mo. 

44. Hanovia Chemical & Mfg. Co., 
Newark, N.J. 

45. Holophane Co. Inc., New York 

46. Hyatt Bearings Div., General 
Motors Corp., Harrison, N. J., 
Engineering Handbook 

47. I.C.S. Electric Signs, Weitz, Int. 
Textbook Co., Scranton, Pa. 

48. Illuminating Engineering Society, 
London, England. 

49. Indiana Service Co., Fort Wayne, 
Indiana. 

50. Inst, of Traffic Engineers, New 
Haven, Conn. 

51. Industry Committee on Wiring 
Design, New York, N. Y. 

52. Intersociety Color Council, Wash- 
ington. D. C. 



53. Thomas Smith Kelly, New York 

54. F. P. Kuhl, New York, N. Y. 

55. Emil Kun, E. E., New York 

56. Leeds & Northrup Co., Phila. Pa. 

57. Lighting & Lamps, New York, N. Y. 

58. Line Material Co., East Strouds- 
burg, Pa. 

59. Macbeth Corp., New York, N. Y. 

60. McGraw-Hill Book Co. Inc., New 
York,N.Y. 

a. The Principles of Optics, Hardy 
& Perrin. b. Scientific Basis of 
Illuminating Engineering, Moon, 
c. Measurement of Radiant 
Energy, Forsythe. d. Standard 
Handbook for Electrical Engi- 
neers, Knowlton. 

61. Metropolitan Edison Co., Reading, 
Pennsylvania. 

62. The Miller Co., Meriden, Conn. 

63. Mitchell Mfg. Co., Chicago, 111. 
64- Mole Richardson Inc., Hollywood, 

Calif. 

65. Monsanto Chem. Co., St. Louis, Mo. 

66. Munsell Color Co., Baltimore, Md. 

67. National Bureau of Standards, 
U. S. Dept. of Commerce, Wash- 
ington, D. C. 

68. National Carbon Co., Cleveland, 0. 

69. National Electrical Code, National 
Fire Protection Assn., Boston, Mass. 

70. National Electrical Manufacturer's 
Assn., New York, N. Y. 

71. National Technical Laboratories, 
South Pasadena, Calif. 

72. New Orleans Public Service, Inc., 
New Orleans, La. 

73. Northwestern Electric Co., Port- 
land, Oregon. 

74- Pan American World Airways 
System, New York, N. Y. 

75. Pennsylvania Power & Light Co., 
Allentown, Pa. 

76. Philadelphia Electric Co., Phila- 
delphia, Pa. 

77. Geo. P. Pilling & Son Co., Phila- 
delphia, Pa. 

78. Pittsburgh Reflector Co., Pitts- 
burgh, Pa. 

79. Polaroid Corp., Cambridge, Mass. 

80. Prismo Safety Corp., Huntingdon, 
Pennsylvania. 

81. Public Service Electric & Gas Co., 
Newark, N. J. 

82. Pyle National Co., Chicago, 111. 

CREDITS 

Section 1. 

1-5: 109. 1-7: 60a. 1-S: 
65. 1-10: 68. 1-11: 108. 
1-14: 108. 1-16: 108. 



60b. 
1-13: 



1-9: 

108. 



83. Radio Corp. of Amer., Harrison, 
New Jersey. 

84. Rambusch Decorating Co., N. Y. 

85. Rochester Gas & Electric Co., 
Rochester, N. Y. 

86. Russell & Stoll Co. Inc., New York 

87. J. G. Saltzman Inc., New York 

88. George S. Sharp, Naval Architect, 
New York, N. Y. 

89. Singer Sewing Machine Co., N. Y. 

90. Sioux City Gas & Electric Co., 
Sioux City, Iowa 

91. Society of Automotive Engineers 
Inc., New York, N. Y. 

92. Southwestern Gas & Electric Co., 
Shreveport, La. 

93. Star Headlight & Lantern Co., 
Rochester, N. Y. 

94. Stimsonite Plastics, Chicago, 111. 

95. Sylvania Electric Products Inc., 
New York, N. Y. 

96. Thompson Elect. Co., Cleveland, O. 

97. Union Metal Mfg. Co., Canton, O. 

98. Union Switch & Signal Co., Swiss- 
vale, Pa. 

99. United Airlines, New York, N. Y. 

100. U. S. Dept. of Agric. Wash., D. C. 

101. U. S. Navy Dept., Wash., D. C. 

102. D. Van Nostrand Co. Inc., New 
York, N. Y. 

a. Light Vision & Seeing, Luckiesh. 

b. The Science of Seeing, Luckiesh 
&Moss. c. Applications of Germ- 
icidal, Erythemal & Infrared En- 
ergy, Luckiesh. 

103. Voigt Co., Philadelphia, Pa. 

104. F. W. Wakefield Brass Co., Ver- 
milion, Ohio 

105. Western Cataphote Corp., Toledo, O. 

106. Western Union Telegraph Co.,N. Y. 

107. Western United Gas & Electric 
Co., Aurora, 111. 

108. Westinghouse Electric Corp., 
Bloomfield, N. J., Cleveland, Ohio 

109. Weston Electrical Instrument 
Corp., Newark, N.J. 

110. West Penn Power Co., Pittsburgh, 
Pennsylvania. 

111. John Wiley & Sons Inc., New York, 
N. Y., Electrical Engineers' Hand- 
book, Pender, Del Mar 

112. R & W Wiley, Inc., Buffalo, N. Y. 

113. Wilmot Castle Co., Rochester, N. Y. 

114. Wiremold Co., Hartford, Conn. 

(Illustration) 

Section 2. 

2-1: 102b. 2-10:48. 2-11 :48. 2-12 48. 
2-14a: 38. 2-15: 102a. 2-16a: 102b. 2- 
19: 60b. 



Section 4. 

4-la, c: 76. 4-3: 28. 4-5: 66. 4-11 
52. 4-llb: 100. 4-12: 100. 4-14a: 88 
b:71. 4-15:78,38. 4-16:3. 
Section 5. 

5-4: 70. 5-5: 109. 5-7a: 5tf. b 
5-8: 38. 5-9: 32. 5-11: 32. 5-12 
5-13: 67. 
Section 6: 

6-1: 38. 6-5: 38, 95. 6-7 



88. 
67. 



95. 



38. 6-10:38. 

38. 6-16: 38. 

38. 6-21:35. 

24: 38. 6-25 



6-12 
6-17 
6-22 
38. 



6-14 :■ 
6-18:, 



6-31:38. 6-32:55. 
6-35: 95. 6-36: 95. 
108,38. 
Section 7: 

7-7:36. 7-8: 60a. 
18. d-h: 8. 7-16: 
79. 7-21:79. 
Section 8: 

8-2: 38. 8-3: 38. 
8-6: 38. 8-7: 38. 
8-11: 95, 33. 8-12: 38 
14:38. 8-15:606. 8-16 
Section 9: 

9-1:^. 9-3:25. 9-4:25. 
Section 10. 

10-1: 104. 10-2:107. 
38. 10-6:108. 10-7a: 5 
20. 10-9: 84- 10-10: 
10-12:37. 10-13:^3. 
15: 5. 10-16: 3/. 



6-9 
6-15 
6-20 

108. 6-23: 106. 6- 

6-26: 38. 6-27: 38. 

6-33: 95. 6-34: 95. 

6-39:95. 6^1:95, 



7-12a,b: 45 

. 7-17: 38. 7-20 



8-4: 3* 
8-9: 45. 



8-5: 
8-10: 

8-13: 708. 
60b. 



9-5:25. 9-6:25. 

10-3:35. 10-4: 

S. b:53. 10-8: 

49. 10-11: /5. 

10-14:75,62. 10- 

10-17: 30. 10-19: 



108. 10-20: 96. 10-21: 
b: 30. c: 708. 10-23a, b: 
10-24: 4- 10-32: 73. 10-33 
108. 10-35a, b: 708. c: 22. 
22. 10-37: 45. 10-3S: 13. 
10-40: 75, 703. 10-41: 30, 
30, 85,81. 10-43: 2. 10-45: 
73, 76, 704- 10-47: 27, 30, 
SO. 10-49: 38. 10-50 
10-52: 2. 10-53a: 708. 
708. 10-56a: 108. b: 10. 
10-58: 84, 37. 10-60: 38. 



c,d: 1 



95, 38. 10-222., 

38. c: 30. 

11. 10-34: 

10-36: 704, 

10-39: 43. 

95. 10-42 

703. 10-46 

37. 10-48 

(bottom) 43 

b: 43. 10-55 

10-57: 770 

10-61: 38 

CREDITS 



2-2: 
4-1: 



7026. 



6-4: 



Section 2. 
Section 4. 
Section 6. 

6-1 : 38 
34. 6-11:38. 
Section 8. 

8-1: 708. 8-2: 708. 
708. 8-5:708. 8-8:38. 
38. 8-12:38. 8-13:38. 
38. 8-16:38. 



6-7: 706. 6-10: 



S-3: 708. 

8-10:38. 

8-14:45. 



8-4 
8-11 
8-15 



Section 9. 
Section 10. 

10-2:57. 
Section 11. 

11-1: 47. 



9-1:25. 9-2:25. 9-3:25. 



10-4: 57. 10-5:57. 10-6:57. 



11-2: 47. 11-3: 47. 11-4: 



10-62:72,84,43,24. 10-63:76,84- 10- 
65: 773. 10-66: 62. 10-67: 38. 10-68: 

37. 10-69:30. 10-70:38,70,35. 10-75: 

38. 10-79: 43. 10-80: 70. 10-81: 708. 
10-82: 62. 10-84: 38. 10-96: 55. 
Section 11. 

11-1:47. 11-2:47. 11-3:708. 11-4: 
47. 11-5:47. 11-6:47. 11-10:47. 11- 
11: 47. 11-13: 47. 11-14: 47. ll-16a 
78. b: 79. c: 87. d: 38, 78. 11-17 
90. 11-18: 38. 11-20: 79, 87. ll-21a 
38. b: 79, 11-23: 708. 
Section 12: 

12-1: 708. 12-2a, b: 70. c: 38. 12- 
3a: 54. b, c: 708. 12-14a: 70. 12-5 
708, 38. 12-6: 20. 12-7: 70. 12-8: 70 
b: 97. 12-9: 708. 12-12: 70. 12-13 
70. 12-14a: 70. b, c: 97. 12-15a: 70 

108. 12-16: 70. 12-17: 70S. 
Section 13. 

13-1: 38. 13-2: 97. 13-3: 97. 13-4 
97. 13-5:97. 13-6:97. 13-8:38. 13-9 
38. 13-10: 38. 13-11: 38. 13-12: 38 
13-13:38. 13-14:38. 13-15:82. 13-16 
99. 13-17: 99. 13-18: 38. 13-19: 86 
88. 13-20: 86. 13-21: 708. 13-22:707 
13-23:80. 13-24:94. 13-25:94. 13-26 
705. 13-33: 30, 108, 58, 38. 13-36: 708 
13-37: 74, 79. 13-38: 74- 13-39: 74 
13-40:74. 13-41:74,708,95. 13-42:74 
13-46:78. 13-47:26,93. 13-48:98. 13- 
51:7. 
Section 14. 

14-2: 38. 14-3a: 87. b: 95. c: 38 
14-4:68,64,38. 14-5:73. 14-6:73. 14 
8: 73. 14-9: 28. 14-10: 64. 14-11: 38 
14-12:38. 14-13:83. 
Section 15. 

15-1:38. 15-2:38. 15-4:89. 15-5:38 
15-6:9. 15-7:38. 15-8:38. ] 5-9: 77. 
Section 16. 

16-1: 38. 16-2: 60c. 16-3: 38, 108 
16-4: 38. 16-5: 38. 16-6: 708. 16-7 
95, 44, 38, 108. 16-8: 702c. 16-9: 708 
16-10: 38. 16-11: 6. 16-12: 95. 16-14 
35. 16-15:38. 16-16:38. 

(Table) 

47. 11-5: 47. 11-6: 87. 11-7: 38. 11- 
8: 7. 11-9: 708. 11-10: 47, 108. 11-11 
47, 108. 11-13: 87. 11-14: 708. 
Section 13. 

13-1:38. 13-2:708. 13-3:50. 13-11:78 
Section 14. 

14-7:38. 14-9:38. 14-10:68. 14-11:38 
Section 15. 15-2: 67. 
Section 16. 16-1:38. 16-4:38. 16-6:38 
Appendix. 

A-5: 69. A-6: 69. A-7: 57. A-S: 69, 
A-9:57. A-ll:3. A-13: 3. A-18 : 60d 
A-19: 46. A-26: 777. A-27: 46. A-28 
46. A-29:46. 



SECTION 1 

I THE PHYSICS OF LIGHT PRODUCTION 

v 

The American Standards Association and the Illuminating Engineering 
Society define light asiradiant energy evaluated according to its capacity to 
'produce visual sensationS Radiant energy of the proper wavelength makes 
visible anything from which it is emitted or reflected in sufficient quantity 
to activate the receptors in the eye. 

( Several concepts of the nature of radiant energy have been advanced. 1 
They are : 

A. The corpuscular theory advocated by Newton, based on these premises: 

1 . That luminous bodies emit radiant energy in particles. 

~~ 2. That these particles are intermittently ejected in straight lines. 
— 3. That the particles act on the retina of the eye stimulating the optic 
nerves to produce the sensation of light. 

— B. The wave theory) based on these premises: 

~ 1. That light is the resultant of molecular vibration in the luminous 

— material. 

2. That vibrations are transmitted through the ether as wavelike move- 
ments (comparable to ripples in water). 

3. That the vibrations thus transmitted act on the retina of the eye 
stimulating the optic nerves to produce visual sensation. 

C. The electromagnetic theory , 2 based on these premises: 

— 1. That luminous bodies emit light as a form of radiant energy. 

--2. That this radiant energy is transmitted in the form of electromagnetic 
-_ waves. 
3. That the electromagnetic waves act upon the retina of the eye thus 
stimulating the optic nerves to produce the sensation of light. 

D. The quantum theory, a modern form of the corpuscular theory, based 
on these premises: 

"~ 1. That energy is emitted and absorbed in discrete quanta. 
2. That the magnitude of each quantum is hv, 

where h — 6.547 X 10~ 27 erg sec (Planck's constant) 
and v = frequency in cycles per second. 

E. The theory of wave mechanics first proposed by Schrodinger in 1925 
in an attempt to reach an harmonious compromise between the quantum 
and the wave theories. 

1. It utilizes wave characteristics and quanta particles as the need arises 
in the solution of problems. 

2. The mathematics involved is too complicated for present application 
to illuminating engineering problems. 

Note: References are Listed at the end of each section. 

1-1 



1-2 



I E S LIGHTING HANDBOOK 



Until such time as new data or concepts are available the quantum 
and the electromagnetic wave theories will unquestionably be used as the 
basis of continued research in light phenomena. The electromagnetic 
wave theory provides a convenient explanation of those characteristics 
of radiant energy most frequently of concern to the illuminating engineer. 

Radiant energy may be evaluated in a number of different ways; two 
of these are: 

1. Radiant flux — the time rate of the flow of any part of the radiant 
energy spectrum measured in ergs per second. 

2. Luminous flux — the time rate of the flow of the luminous parts of the 
radiant energy spectrum measured in lumens. 

Light and the Energy Spectrum 

The wave theory permits a convenient graphical representation of 
radiant energy in an orderly arrangement according to its wavelength. 
This arrangement is called a spectrum (Fig. 1-1). It is useful in indicating 
the relationship between various radiant energy wavelength regions. 
Such a graphical representation must not be construed to indicate that 
each region of the spectrum is divided from the others in any physical way 
whatsoever. Actually there is a gradual transition from one region to 
another. 

FREQUENCY IN CYCLES PER SECOND 



\ 



COSM IC RAYS 
GAMMA RAYS 



X-RAYS 
HARD SOFT 



HERTZIAN WAVES 



VAC UUM U.V. 
ULTRAVIOLET •— * 



* INFRARED 
NEAR FAR 



- DIRECTIONAL 
RADIO (RADAR) 



FM 
TELEVISION 



VIOLET BLUE GREEN YELLOW RED 



_ SHORT 
WAVE 



0.5 0.6 0.7 

WAVELENGTH IN MICRONS 



I X-UNn" I ANGSTROM 



0.76 BROADCAST 

I CM I METER I KILOMETER 



POWER 
TRANS- 
MISSION 



,0-12 10 -I0 io-8 



I0"6 10"4 10"2 ] io2 

WAVELENGTH IN CENTIMETERS 



I0 4 



I0 6 



I0 8 



10'0 



FIG. 1-1. The radiant energy (electromagnetic) spectrum. 



The known limits of the radiant energy spectrum extend over a range 
of wavelengths varying from a few micromicrons (10~ 10 cm) to one hundred 
thousand miles (1.6 X 10 10 cm). Radiant energy in the visible spectrum 
has wavelengths betAveen 0.38 X 10~ 4 and 0.76 X 10~ 4 cm. 

The Angstrom unit (A), the micron (/x), and the millimicron (m/x) are 
commonly used units of length in the visible spectrum band. The rela- 
tionship of several units for measuring wavelength is given in Table 1-1. 



PHYSICS OF LIGHT PRODUCTION 



1-3 



All forms of radiant energy are transmitted at the same rate of speed 
in vacuum (186,300 miles per second). However, each form differs in 
wavelength and thus in frequency. The wavelength and velocity may be 
altered materially by the medium through which it passes, but frequency 
is fixed independently of the medium. Thus, through the equation: 

V = n\v 
where V = velocity of waves (cm per sec) 
n — (index of refraction) 
X = wavelength (cm) 
v — frequency (c per sec) 

it is possible to determine the velocity of radiant energy and also to indicate 
the relationship between frequency and wavelength. 

Table 1-2 gives the velocity of light in different media for a frequency 
corresponding to a wavelength of 0.589 micron in air. 



Table 1-1. Conversion Table for Units of Length 



Multiply Number 
















C/3 




of ► 














OS 

w 

H 


(A 

w 

H 


Pi 
W 


■& 


O 


w 










w 


W 


H 


p4 


fc 




C/3 








g 


W 


To Obtain \ 


H 
en 


o 
PS 






H 




H 


S 


Number of \ 

1 \ 


O 


u 


H 


(J 


W 


kJ 


J 


g 




% 


§ 


§ 


g 




S 


S 




w 


ANGSTROMS 


1 


104 


2.540 
XIO 5 


2.540 

X108 


3.04S 

X109 


1.609 
XIO" 


10 7 


108 


lOU 


MICRONS 


10-4 


1 


2.540 

xio 


2.540 
X104 


3.048 

xio* 


1.609 
X10' 


103 


104 


109 


MILS 


3.937 


3.937 


1 


103 


1.2 


6.336 


3.937 


3.937 


3.937 




X10-6 


X10-2 






X104 


XIO 7 


xio 


X102 


X10 7 


INCHES 


3.937 


3.937 


10-3 


1 


12 


6.336 


3.937 


3.937 


3.937 




xio-» 


XlO-s 








XW 


X10-2 


xio-' 


X104 


FEET 


3.281 


3.281 


8.333 


8.333 


1 


5.280 


3.281 


3.281 


3.281 




X10-' 8 


X10" s 


X10-5 


X10-2 




X10» 


X10-3 


X10-J 


X103 


MILES 


6.214 


6.214 


1.578 


1.57S 


1.894 


1 


6.214 


6.214 


6.214 




XlO-n 


X 10-19 


XIO" 8 


XlO-s 


X10-4 




xio-' 


xio-« 


xio-' 


MILLIMETERS 


lO-' 


10-3 


2.540 


2.540 


3.04S 


1.609 


1 


10 


10 6 








X10-2 


X10 


X102 


XIO 8 








CENTIMETERS 


10-8 


10-4 


2.540 
XIO"' 


2.540 


3.048 

xio 


1.609 
X10* 


0.1 


1 


10» 


KILOMETERS 


10-" 


10-9 


2.540 
XIO"' 


2.540 

xio-» 


3.048 
X10-4 


1.609 


io-« 


10" s 


1 



Table 1-2. Velocity of Light for a Wavelength of 0.589 Micron 

(Sodium D-lines) 



MEDIUM 


VACUUM 


AIR (760 mm 0°C) 


CROWN GLASS 


WATER 


VELOCITY 
(cm per see) 


(2.99776 ± 0.00004) X 10" 


2.99708 X lOio 


1.98212 X 10" 


2.24903X1010 



1-4 



I E S LIGHTING HANDBOOK 



Luminosity of Radiant Energy 

The apparent differences in character between radiant energy of various 
wavelengths are in reality differences in ability of various receiving and 
detecting devices. 3 

The reception characteristics of the human eye have been subject to ex- 
tensive investigations. The results may be summarized as follows: 

1. The spectral response characteristic of the human eye varies between 
individuals, with time, and with the age and the state of health of any indi- 
vidual, to the extent that the selection of any individual to act as a standard 
observer is not scientifically feasible. 

2. However, from the wealth of data available, a luminosity curve 
has been selected for engineering purposes which represents the average 
human observer. This curve may be applied mathematically to the solu- 
tion of photometric problems so as to eliminate the disadvantages related 
to all measurements dependent on the accurate reporting of human sensa- 
tions. (See also Section 2.) 

Recognizing these facts, the Illuminating Engineering Society in 1923 
and the International Commission on Illumination (I.C.I.) in 1924 adopted 
the standard luminosity factors of Table 1-3 from which the luminosity 
curve of Fig. 1-2 was plotted. 

Table 1-3. Standard Luminosity Factors 

(Relative to unity at 0.554 micron wavelength)*' 



WAVELENGTH 


FACTOR 


WAVELENGTH 


FACTOR 


WAVELENGTH 


FACTOR 


(micron) 




(micron) 




(micron) 




0.380 


0.00004 


0.510 


0.503 


0.640 


0.175 


.390 


.00012 


.520 


.710 


.650 


.107 


.400 


.0004 


.530 


.862 


.660 


.061 


.410 


.0012 


.540 


.954 


.670 


.032 


.420 


.0040 


.550 


.995 


.680 


.017 


.430 


.0116 


.560 


.995 


.690 


.0082 


.440 


.023 


.570 


.952 


.700 


.0041 


.450 


.038 


.580 


.870 


.710 


.0021 


.460 


.060 


.590 


.757 


.720 


.00105 


.470 


.091 


.600 


.631 


.730 


.00052 


.480 


.139 


.610 


.503 


.740 


.00025 


.490 


.208 


.620 


.381 


.750 


.00012 


.500 


.323 


.630 


.265 


.760 


.00006 



1 Luminosity factor = 1.0002 for 0.555 micron is maximum. 



The standard luminosity curve represents an average characteristic 
from which the characteristic of any individual may be expected to vary. 
Goodeve's data (Fig. 1-3) indicate that most human observers are capable 
of experiencing a visual sensation upon exposure to radiation of infrared 
wavelengths (longer than 0.76 micron). It also is known that observers 
exhibit a slight response to ultraviolet wavelengths (shorter than 0.38 
micron). 



PHYSICS OF LIGHT PRODUCTION 



1-5 



VIOLET BLUE GREEN 
1.0 



0.9 
0.8 



£0.5 

5 

D 

J 0.4 

> 

<0.3 

_l 

LU 

<r 

0.2 






0.1 



0.38 0.42 0.46 0.50 0.54 0.58 0.62 0.66 0.70 0.74 
WAVELENGTH OF RADIANT ENERGY IN MICRONS 

1 micron =10,000 angstroms = 1/10,000 centimeter 

FIG. 1-2. The standard (I.C.I.) luminosity 
curve shows the relative capacity of radiant 
energy of various wavelengths to produce 
visual sensation. 



10-2 



I0" 4 




0.70 0.75 0.80 0.85 0.90 
WAVELENGTH IN MICRONS 

FIG. 1-3. Goodeve's investi- 
gations reveal that high flux con- 
centrations of wavelengths just 
outside the "visible region" are 
capable of producing visual sen- 
sations. 7 



Photoelectric Effect 

This phenomenon, which may be observed when a clean metal surface 
is illuminated, is the liberation of electrons from the surface atoms. If 
the surface is connected as a cathode in an electric field (Fig. 1-4) the lib- 
erated electrons will flow to the anode creating a photoelectric current. 
An arrangement of this sort may be used as an illumination meter and can 
be calibrated in f ootcandles. 



CATHODE 
(METAL PLATE)""-, 



--X 



LIGHT QUANTUM 
(ENERGY = hV) 



— 

ELECTRON 
(ENERGY = Vz mV 2 = hV-E ) 




ANODE 



ENERGY TO-' 

RELEASE 

ELECTRON =E 



FIG. 1-4. By the photoelectric effect, electrons may be liber- 
ated from illuminated metal surfaces. In an electric field these 
will flow to an anode and create an electric current which may be 
detected by means of a galvanometer. 




1-6 I E S LIGHTING HANDBOOK 

Effect of illumination. It has been found that the photoelectric current 
in vacuum varies directly with the illumination over a very wide range 
(spectral distribution, polarization, and cathode potential remaining the 
same). In gas-filled tubes the response is linear over only a limited range. 

Effect of polarization. If the illumination is polarized, the photoelectric 
current will vary as the orientation of the polarization is changed (except 
at normal incidence). 

Effect of wavelength. The more electropositive the metal the longer the 
wavelength of its maximum photoelectric emission and the lower the fre- 
quency threshold below which electrons are not liberated. (See Table 1-4.) 

Table 1-4. The Electrode Potential Series 

Li Rb K Cs Na Ba Sr Ca Mg Mn Zn Cr Fe* Cd Tl Co Ni Sn Pb Fef Sb Bi As Cu Ti Pt Hg Ag Au 
HIGH LOW 

* ferrous t ferric 

The maximum value of the initial velocity of a photoelectron and there- 
fore its maximum kinetic energy decrease as the wavelength of the illumina- 
tion increases. 

The quantum theory provides the energy relationships which explain 
this phenomenon. The energy E of a light quantum equals the product 
of Planck's constant h by the frequency v. 

E = hv 

It is known that an amount of energy E (different for each metal) is 
required to separate an electron from the atom with which it is associated. 

Therefore, the energy of the liberated electron {\mv 2 ) is equal to that 
of the incident quantum hv lessE'o, that required to free it from the metal: 

i mt ,2 _ fa _ j g' 

where m — mass of electron 

v = velocity of electron 

The barrier layer or 'photovoltaic cell, when illuminated, generates voltage 
even though not connected to an external power source. The cell com- 
prises a metal plate coated with a semiconductor (selenium on iron or 
cuprous oxide on copper, for example). Upon exposure to light, electrons 
liberated from the metal surface are trapped at the interface unless there 
is an external circuit provided through which they may escape. In photo- 
graphic and illumination meters, this circuit includes a small microam- 
meter calibrated in units of illumination. (See Fig. 1-5.) This type is 
commonly used in photographic exposure meters and portable illumina- 
tion meters. 



PHYSICS OF LIGHT PRODUCTION 



1-7 



Light Production 

Light may be produced in many ways and by several types of devices 
tabulated under two broad headings: 



1. Incandescence 
Combustion 
Arc electrodes 
Gas mantle 
Lamp filament 
Radiant heater 



Luminescence 
Arc stream 
Gaseous discharge 
Glow discharge 
Fluorescence 
Phosphorescence 
Cathodoluminescence 
Chemiluminescence 
Triboluminescence 



INCIDENT 
SEMI- LIGHT 

TRANSPARENT 
CATHODE 
, 1 

\ 



LIBERATED- 
ELECTRON 



LIOHI 



SURFACE 
RESISTANCE 



-VW 



•.••;:•::: SEMI -'•••.•: 

CONDUCTOR 



METAL BASE 



••■:■ INTERNAL^ •-. 
; CAPACITANCE' 



ABSORBED BY WALLS 




FIG. 1-5. Cross section of barrier layer or photo- 
voltaic cell showing motions of photoelectrons through 
microammeter circuit. 



FIG. 1-6. Small aperture 
in an enclosure exhibits 
blackbody characteristics. 



The physical phenomena associated with light production by these means 
are best explained by Planck's quantum theory and by the modern atomic 
theories first conceived by Bohr and Rutherford. 

Incandescence 

Familiar physical objects are simple or complex combinations of chemi- 
cally identifiable molecules, which in turn are made up of atoms. In 
solid materials the molecules are packed together and the substances hold 
their shape almost indefinitely over a wide range of physical conditions. 
In contrast, the molecules of a gas are highly mobile and occupy only a 
small part of the space filled by the gas. 

Single molecules and atoms are much too small (3 X 10 -8 cm) to be 
observed directly, but much is known of their characteristics. 

Molecules of both gases and solids are constantly in motion and their 
movement is a function of temperature. If the solid or gas is hot, the 
molecules move rapidly; if it is cold, they move more slowly. 

At temperatures below about 573 degrees Kelvin (300 degrees Centi- 
grade) invisible energy of the longer infrared (heat) wavelengths is emitted 



1-8 I E S LIGHTING HANDBOOK 

by any body, a coal stove or an electric iron, for example. The jostling 
of the molecules at temperatures above 300 'degrees Centigrade results 
in the release of visible radiation along with the heat. Molecular activity 
in the filament, caused by the heating action of the electric current, results 
in the production of light by the incandescent electric lamp. 

Blackbody Radiation 

The light from practical light sources, particularly that from incandescent 
lamps, is often described by comparison with that from a blackbody or 
complete radiator. Defined as a body which absorbs all of the radiation 
incident upon it, transmitting none and reflecting none, a blackbody will 
for equal area radiate more total power and more power at any given wave- 
length than any other source operating at the same temperature, unless 
that source radiates energy b}' some phenomenon other than temperature. 

For experimental purposes, laboratory sources have been devised which 
approach the ideal blackbody very closely in output characteristics. All 
of the many different designs are based on the fact that a hole in the wall 
of a closed chamber, small in size as compared with the size of the enclosure, 
is absolutely black. This is understood if one considers what happens to a 
ray of light entering such an enclosure. (See Fig. 1-6.) Assuming the 
reflectance of the walls to be low, the incident energy soon will be ab- 
sorbed in the walls by interreflections. 

Recently the brightness of a blackbody operating at the temperature of 
freezing platinum has been established as a new international candlepower 
reference standard. It has the advantage of reproducibility over the bank 
of carbon filament lamps which have been in use for so many years. (See 
footnote on page 1-12, also Section 3.) 

Planck's equation for blackbody radiation was developed, by the intro- 
duction of the concept of radiation of discrete quanta of energ}", to represent 
the radiation curves obtained in 1900 by Lummer and Pringsheim, who 
used the open end of a specially constructed and uniformly heated tube 
as their source. It has the form: 

Wx = Ci\- 5 (e C2/XT - l)- 1 
where W\ = watts radiated by a blackbody (per cm 2 of surface) in 
each wavelength band one micron wide, at wavelength X 
X = wavelength in microns (/x) 

T = absolute temperature of the blackbody (degree Kelvin) 
ci = 36,970* 
c 2 = 14,320* 
e = 2.718+ 

* Improvements made by various investigators in the techniques by which these constants are determined 
result in the publication, from time to time, of slightly different values. 

The following values, which have been used in calculations of the maximum luminous efficiency of ra- 
diant energy accepted by the I. E. S., were published in 1939 by H. T. Wensel in the Journal of Research of 
the National Bureau of Standards: 

c\ = 3.732 X 10" 5 erg cm* second"* 
c; = 1.436 cm degree 
a = 5.70 X 10 -6 erg cm -2 degree"* second" 1 
(See footnote page 1-12) 
The most recent values, published in 1941 by R. T. Birge in Reviews of Modern Physics, are: 
ci = 3.738 X 10-& erg cm 2 second"! 
a = 1 .438<8 cm degree 
a — 5.6728) X 10 -5 erg cm" 2 degree -4 second -1 



PHYSICS OF LIGHT PRODUCTION 



1-9 



The curves for several values of T are plotted on a logarithm scale in 
Fig. 1-7. 



WIEN DISPLACEMENT OF WAVELENGTHS 

OF MAXIMUM RADIATION 

I* »1 



I0 8 



wio' 



IlO 5 - 



5 10 4 
o 

a. 

^103 
< 
Q _ 

< 10 2 

* 



-l-VISIBLE 
REGION 




1000 



O400 

cr 

o 



100 



- 


















- 


















- 










BLACKBODY 


- 


























*'*< 


,GRAY- 
{ BODY 


— 










\\ 








- 










\\ 








- 


















- 




















\ 










\\ 






- 


\ 










V 


\ 




- 


/ 












' \ 




- 




SELECTIVE \ 
RADIATOR V 
(TUNGSTEN) 






- 




\ 
\ 

\ 






I 


1 








i 


l 





O.t 1 

WAVELENGTH 



1 micron = 10,000 angstroms = 1/10,000 centimeter 

FIG. 1-7. Blackbody radiation curves for 
operating temperatures between 500 degrees 
Kelvin and 20,000 degrees Kelvin showing Wien 
displacement of peaks. Shaded area is region 
of visible wavelengths. 



0.1 0.2 0.4 I 2 4 6 8 10 

WAVELENGTH IN MICRONS 

FIG. 1-8. Radiation curves for 
blackbody, graybody, and selective 
radiators operating at 3,000 degrees 
Kelvin. 



Wien radiation law. In the temperature range of tungsten filament 
lamps (2,000 degrees Kelvin-3,400 degrees Kelvin) and in the visible 
Avavelength region (0.38-0.76/z), the following simplification of the Planck 
equation known as the Wien radiation law gives a reasonably accurate 
representation of the blackbody distribution: 

W x = dX- 5 e- C2/Xr 

The Wien displacement law gives the relation between blackbody distribu- 
tions for various temperatures (see line AB, Fig. 1-7) : 

TTx = Ci\- 5 F(\T) 

where F = luminous flux (lumens) the principal corollaries are: 

XmaxT = 6 (2883.6 micron-degrees) 

where X ma x is the wavelength, in microns, at which blackbody radiation is a 

dW 
maximum, found by setting -z— = 0. 

d\ 

W ma xT- 5 - 6i = 1.3 X 10- 11 watt cm" 3 degree" 5 



1-10 I E S LIGHTING HANDBOOK 

The Stefan-Boltzmann law, obtained by integrating Planck's expression 
for W\ from zero to infinity, states that the total radiant power per unit 
area of a blackbody varies as the fourth power of the absolute temperature: 

W = aT* watts per cm 2 
where W = summation of power per unit area radiated by a blackbody 
at all wavelengths 
a = 5.735 X 10~ 12 watt cnr 2 degree -4 (see footnote, page 1-8) 
T — temperature of the radiator (degree Kelvin) 

It should be noted that this equation applies to the total power, that is, 
the whole spectrum. It cannot be used to estimate the power in the visible 
portion of the spectrum alone. 

Graybody Radiation 

A radiator which does not emit as much power as a blackbody but which 
has exactly the same spectral distribution is known as a graybody. 

The ratio of its output at any wavelength to that of a blackbody at the 
same wavelength is known as the spectral emissivity (e\) of a radiator. No 
known radiator has a constant spectral emissivity for all visible, infra- 
red, and ultraviolet wavelengths, but in the visible region a carbon fila- 
ment exhibits very nearly uniform emissivity, that is, is nearly a graybody. 

Selective Radiators 

The emissivity of all known materials varies with wavelength. There- 
fore, they are called selective radiators. 

Drude equation. Values of spectral emissivity e\ at wavelengths greater 
than 2 microns may be calculated with reasonable accuracy by means of 
the Drude equation: 

ex - 0.365,4/1 

where p = the electrical resistivity of the emitting material (ohm-cm) 
X = wavelength (cm) 

For shorter wavelengths, at which the resistivity is a function of the fre- 
quency of the emitted wavelengths, the Drude equation does not give good 
results and the emissivity must be determined experimentally. 

Blackbody, graybody, and selective radiator comparison. In Fig. 1-8 
the radiation curves for a blackbody, a graybody, and a selective radiator 
(tungsten), all operating at 3,000 degrees Kelvin, are plotted on the same 
logarithm scale to show the characteristic differences in output. 

Radiation equations into which the spectral emissivity factor has been 
introduced are applicable to any incandescent source : 



PHYSICS OF LIGHT PRODUCTION 1-11 

Planck's equation: Wx = 30,970 e x X _5 (10 621910/Xr - l)" 1 (See foot- 

Wien radiation law: Wx = 30,970 e x X" 5 10 ~ 621910/Xr note ' 

page 

Stefan-Boltzmann law: W = 5.735 X 10 _12 e, T 4 1-8) 

exWxd\ 



where e t — — ^ (total emissivity) 



I 



W\ dX 



The arc lamp radiates both because of the incandescence of the anode 
and by the luminescence of vaporized electrode material in the arc stream. 
By varying the electrode materials considerable spread in the spectral 
distribution and high brightness may be achieved. 

Color Temperature 

The radiation characteristics of a blackbody of unknown area may be 
specified with the aid of the equations on page 1-8 by fixing only two 
quantities: the magnitude of the radiation at any given wavelength and 
the absolute temperature. The same type of specification may be used 
with reasonable accuracy for tungsten filaments and other incandescent 
sources. However, the temperature used in the case of selective radiators 
is not that of the filament but a value called the color temperature. 

The color temperature of a selective radiator is equal to that temperature 
at which a blackbody must be operated if its output is to be the closest 
possible approximation to a perfect color match of the output of the 
selective radiator. (See also Section 4.) While the match is never ab- 
solutely perfect the small deviations which occur in the case of incandes- 
cent lamps are not of practical importance. 

The apertures between coils of the filaments used in many tungsten 
lamps act somewhat as a blackbody because of the interreflections which 
occur at the inner surfaces of the helix formed by the coil. For this 
reason the distribution from coiled filaments exhibits a combination of the 
characteristics of the straight filament and of a blackbody operating at the 
same temperature. 

The application of the color temperature specification to luminescent 
rather than incandescent sources may result in appreciable errors. 

Efficiency 

The efficiency of a device with respect to the storage, transfer, or trans- 
formation of a physical quantity is defined for most engineering purposes 
as the ratio of the useful output of the quantity to its total input, the out- 
put and input usually being expressed in units of power. 

The efficiency of a light source is defined as the ratio of the total luminous 
flux (lumens) to the total power input (watts or equivalent). 



1-12 I E S LIGHTING HANDBOOK 

Effect of spectral distribution. Since most of the energy radiated by 
incandescent sources is of the long invisible infrared wavelengths, the 
achievable efficiencies are low as compared with the theoretical maximum 
(G50 lumens per watt) that would be obtained if all of the power input were 
emitted as green light of 0.5550 micron wavelength for which the luminosity 
factor is greatest.* 

Because of the shift with increases in temperature from the infrared to 
shorter wavelengths of the maximum of the radiation curve, efficiency may 
be increased by operating lamps at higher temperatures. 

Effect of material characteristics. In practical lamps the rate of evapora- 
tion and the melting point of the filament limit the extent of such gains. 
The melting point of tungsten is 3,655 degrees Kelvin, the highest of all 
metallic elements. 

Because evaporation of the filament at temperatures approaching the 
melting point is great enough to cause unreasonably short life and much 
bulb blackening, it is necessary to operate practical lamp filaments at tem- 
peratures well below the melting point. However, even if it were possible 
to go much higher than known filament materials allow, the efficiency would 
not greatly exceed the maximum of 85 lumens per watt achievable with 
blackbody radiators operating at the optimum temperature of about 6,500 
degrees Kelvin, because much of the energy is radiated outside the visible 
region. 

The maximum attainable efficiency of any white light source (whether it 
be a blackbody, tungsten, gaseous discharge, or fluorescent type) with its 
entire output distributed uniformly with respect to wavelength within the 
visible region, is of the order of 200 lumens per watt. 

Efficiencies greater than 200 lumens per watt can be obtained but only 
from sources of which the entire output approaches concentration in the 
green wavelength of the maximum luminosity factor. 

Maximum attainable brightness. From a superficial consideration of the 
matter it may appear that the brightness of an illuminated surface might 
be raised to any desired value merely by concentrating light upon it from 
a sufficient number of sources. The fact remains that the attainable 
brightness is limited by the attainable brightness of the available light 
sources. 

The top limit depends on the optical arrangement. If the arrangement 
does not return significant amounts of radiation to the sources, the maxi- 
mum brightness attainable will be that of the sources. If radiation is 
returned to the sources, the top limit will approach the brightness of a 
blackbody operating at the true temperature of the sources. 

Luminescence 

Whereas the radiation of incandescent sources results from the irregular 
excitation at high temperatures of innumerable molecules interacting on 

*The value adopted by the I.E.S. (650 lumens per watt) is based on: 1. the 1924 I.C.I, luminosity factors; 
2. the second radiation constant in Planck's equations ci = 1.436; and 3. the brightness of a blackbody at the 
freezing point of platinum (58.9 candles per square centimeter). It is consistant with the calculations of 
H.T. Wensel published in 1939 ("Research Paper 1189" J. Research Nat. Bur. Stand.). See note page 1-S. 



PHYSICS OF LIGHT PRODUCTION 



1-13 



each other and is emitted in all wavelengths to form a continuous spec- 
trum, radiation from luminescent sources results primarily from the ex- 
citation of individual atoms so scattered or arranged that each atom is 
free to act without much interference from its neighbors. 

Radiation resulting from the excitation of the electrons of an atom will 
be emitted at one of the series of wavelengths characteristic of that par- 
ticular element. 



* NUCLEUS < 



( MASS = I _ 

PROTONS < Cb 

[ CHARGE = +1 v 

fMASS=l _. 

NEUTRONS^ O 

I CHARGE =0 w 



) 1 

/ / fMASS= „ 

I 9M ELECTRONS < 0.911 X I0" 27 g 

/ t CHARGE = -1 



HELIUM ATOM 



( © ) ( % ) 



"LIGHT" "HEAVY" 

HYDROGEN ISOTOPES 

FIG. 1-9. Structure of the atom showing electron orbits around central nucleus 
Hydrogen isotopes and helium atom are simplest of all atomic structures. 



Atomic Structure 

The atomic theories first proposed by Rutherford and Bohr in 1913 have 
since been expanded upon and verified repeatedly by careful experiment. 
They propose that "each atom is in reality a minute solar system, such as 
that shown in Fig. 1-9. 

The atom consists of a central nucleus possessing a positive charge n 
about which rotate n negatively charged electrons. In the normal state 
these electrons remain in particular orbits or energy levels and radiation 
is not emitted by the atom. 

The nucleus is made up of protons that carry the positive charge and 
neutrons that are approximately equal in mass to the protons but un- 
charged. 

The number of protons in the nucleus is always the same for a given 
element and gives that element its atomic number. 

All the atoms of a given element have the number of protons in the nu- 
cleus equal to the atomic number Z; but they may differ in the number of 
neutrons A-Z. Atomic species so differing are called isotopes, as in the 
case of deuterium or "heavy" hydrogen (Fig. 1-9), which has a neutron 
in its nucleus in addition to the single proton of "light" hydrogen. Simi- 
larly, the isotopes C/-234, U-235, and C/-238 of uranium contain 92 protons 
each but 142, 143, and 146 neutrons respectively. 



1-14 I E S LIGHTING HANDBOOK 

The system of orbits or energy levels in which the electrons are pictured 
rotating about the nucleus is characteristic of each element and remains 
stable until disturbed by external excitation. 

Chemical reactions between the elements involve only the valence elec- 
trons in the outer orbits. 

Light 'production. It is by the proper excitation of the valence electrons 
that visible radiation is produced in luminescence phenomena. 

The Carbon Arc 

Low-intensity arcs. Of the three principal types of carbon arc in com- 
mercial use, the low-intensity arc is the simplest. In this arc, the light 
source is the white-hot tip of the positive carbon. This tip is heated to a 
temperature near its sublimation point (3,700 degrees Centigrade) by the 
concentration of a large part of the electrical energy of the discharge in a 
narrow region close to the anode surface. (See Fig. 1-10.) 

The gas in the main part of the arc stream is extremely hot (in the neigh- 
borhood of 6,000 degrees Centigrade) and so has a relatively high ion dens- 
ity, and good electrical conductivity. The current is carried through this 
region largely by the electrons, since they move much more readily than 
the positive ions because of their small mass. However, equal numbers 
of positive ions and negative electrons are interspersed throughout the arc 
stream, so no net space charge exists, and the only resistance to the motion 
of the electrons is that supplied by frequent collisions with inert atoms and 
molecules. 

Near the anode surface, the conditions are not as favorable for the con- 
duction of current. The electrode tip is about 2,000 degrees cooler than 
the arc stream, and the gas immediately adjacent consists largely of carbon 
vapor in temperature equilibrium with the surface. At 3,700 degrees 
Centigrade, this carbon vapor is a very poor conductor of electricity. It 
therefore requires a high voltage to force the current-carrying electrons 
through this vapor layer and into the anode. In a pure carbon arc, this 
anode drop is about 35 volts. Most of the heat so developed is transferred 
to the surface of the positive carbon, part by the impact of the highly ac- 
celerated electrons and part by thermal conduction. Finally, as the elec- 
trons reach the anode surface, they release their heat of condensation, 
contributing further to the high temperature of the electrode tip. 

The positive electrode of the low-intensity arc may contain a core con- 
sisting of a mixture of soft carbon and a potassium salt. The potassium 
does not contribute to the light, but does increase the steadiness of the arc 
by lowering the effective ionization potential of the arc gas. 

Flame arcs. A flame arc is obtained by enlarging the core in the elec- 
trodes of a low-intensity arc and replacing part of the carbon with chemical 
compounds known as flame materials, capable of radiating efficiently in a 
highly heated gaseous form. These compounds are vaporized along with 
the carbon and diffuse throughout the arc stream, producing a flame of a 



PHYSICS OF LIGHT PRODUCTION 



1-15 




LOW-INTENSITY ARC 



FLAME TYPE CARBON ARC 




HIGH-INTENSITY ARC 

FIG. 1-10. Low-intensity arc, 30 amperes, 55 volts, direct current. 
Flame arc, 60 amperes, 50 volts, alternating current. (Direct current 
flame arcs very similar.) High-intensity arc, 125 ampei'es, 70 volts, direct 
current (rotating positive carbon). 



color determined by the compounds used. Typical flame materials are 
iron for the ultraviolet, rare earths of the cerium group for white light, 
calcium compounds for yellow, and strontium compounds for red. (See 
Fig. 1-10.) 

Such flame materials have a considerably lower ionization potential than 
carbon. This greater ease of ionization reduces the temperature of the 



1-16 I E S LIGHTING HANDBOOK 

anode layer necessary for the conduction of current into the anode and 
results in a lower anode voltage drop (about 15 volts). The lower anode 
power input reduces the area and brilliance of the anode spot so that its 
contribution to the total light becomes unimportant. The radiation 
emitted by the flame arc consists chiefly of the characteristic line spectra 
of the elements in the flame material and the band spectra of the com- 
pounds formed. The excitation of the line and band spectra is thermal in 
nature, caused by the high temperature of the arc stream gas. The con- 
centration of flame materials in the arc stream is not very high, so that the 
flame arc, while brighter than many other light sources, is considerably 
less bright than either the low or the high intensity arc. Since the whole 
arc flame is made luminous, however, the light source is one of large area, 
and high radiating efficiencies (up to 80 lumens per watt) are obtained. 

High-intensity arcs. The high-intensity arc is obtained from the flame 
arc by increasing the size and the flame material content of the core of the 
anode, and at the same time greatly increasing the current density, to a 
point where the anode spot spreads over the entire tip of the carbon. This 
results in a rapid evaporation of flame material and carbon from the core 
so that a crater is formed. The principal source of light is the crater sur- 
face and the gaseous region immediately in front of it. (See Fig. 1-10.) 
Since the flame material is more easily ionized than the carbon, a lower 
anode drop exists at the core area than at the shell of the carbon. This 
tends to concentrate the current at the core surface, and so encourages the 
formation of the crater. 

The increased brightness of the high-intensity arc is produced by radia- 
tion resulting from the combination of the heav}^ concentration of flame 
materials and the high current density within the confines of the crater. 
Although the primary radiation of this gas is the line spectrum of the con- 
stituent atoms, and the peak intensity of any one line is limited to that of a 
blackbody at the temperature of the crater gas, the energy exchange is so 
intense that the lines are broadened by absorption and re-radiation into a 
partially continuous spectrum. The sum of this continuous and line 
radiation can be so great as to give a brightness over ten times that of the 
low-intensity arc. 

Gaseous Discharges 

The fundamental processes involved in the production of light are the 
same for all types of vapor lamps. The activity in a low-pressure mercury 
discharge tube such as the commercial fluorescent lamp is exemplary of all 
types. 

Ultraviolet radiation from mercury (with the lowest boiling point of all 
metallic elements) used in fluorescent lamps, like the sodium yellow, neon 
red-orange, or cadmium red radiation is the result of changes in atomic 
energy caused by the transition of an electron from one energ}^ state or orbit 
to another. 



PHYSICS OF LIGHT PRODUCTION 



1-17 



Physical activity in a mercury-discharge tube. In Fig. 1-11, a minute 
cross section of a fluorescent lamp has been magnified to show the sequence 
of steps which result in emission of ultraviolet radiation. 

1. A high-speed free or conduction electron boiled off one of the electrodes 
collides with a valence electron of the mercury atom and excites it by knock- 
ing it from its normal energy level to a higher one. 

2. The conduction electron loses speed at the impact and changes direc- 
tion, but may continue along the tube to excite one or more additional 
atoms before completing its path through the lamp. 

3. The valence electron returns presently to its normal energy level and 
liberates by its transition (in this particular instance) a quantum of ultra- 
violet radiation. 



LAMP BULB WALL 



= VISIBLE 
= LIGHT 



gzzzzzzzzz 



^^ 



X 



— ^0 

PATH OF 

CONDUCTION 

ELECTRON 



-^ic y^PHOSPHOR 
r "--"'CRYSTALS 


OtO 
£0 1- 

zz 


ULTRAVIOLET 
RADIATION 


v ELECTRON CLOUD 
\ >.-- OF SINGLE 
X MERCURY ATOM 


uj — 

UJ UJ 

"- > 

U-UJ 

o-J 


D*C AFTER 


— UJ 

ui O 


J) IMPACT 





VALENCE 
ELECTRON -r* 



IONIZING POTENTIAL (10.38) 




FIG. 1-12. Simplified energy diagram 
for mercury showing a few of the char- 
acteristic spectral lines. 



FIG. 1-11. Magnified cross section of 
fluorescent lamp showing progressive steps 
in luminescent process which finally result 
in the release of visible light. 

The wavelengths of radiation emitted depend on the energy transferred 
in the collisions. Radiation may be emitted in any one of several wave- 
lengths (in the ultraviolet, visible, or infrared regions) which are charac- 
teristic of transitions between two mercury energy levels. The wave- 
length varies inversely with the voltage difference in accordance with the 
relationship : 

1 2336 

wavelength X = — microns 

V d 

where V d is the potential difference (volts) between two energy levels 
through which the displaced electron has fallen in one transition. 

This relationship, which applies to luminescence regardless of the ele- 
ments involved, shows that when visible wavelengths are emitted the poten- 
tial difference must be between 3.2 volts for violet (0.380 micron) and 1.6 
volts for red (0.760 micron) light. 

Figure 1-12 is a greatly simplified version of the mercury energ} r level 
diagram showing a few of the possible wavelengths in which energy may be 
radiated from a mercury atom. 



1-18 I E S LIGHTING HANDBOOK 

Complete energy diagrams permit speculation as to the relative desir- 
ability, from the standpoint of luminous efficiency, of using different mate- 
rials in vapor lamps. However, in such a speculation the energy con- 
centrated in each wavelength is equal in importance to the wavelengths 
themselves, and is proportional to the number of transitions occurring per 
second between the voltage difference related to each wavelength. It is a 
function of the number of conduction electrons and valence electrons 
available in the normal state and is difficult to compute. 

Fluorescence and Phosphorescence 

The fluorescent lamp is a relatively simple modification of the ordinary 
mercury lamp. By varying the coating on the inside of the tube a wider 
variety of colors may be obtained conveniently than by merely adjusting 
voltage, pressure, or the gas mixture. 

Upon release from the excited mercury atom (Fig. 1-11), the ultraviolet 
quantum (X = 0.2537 micron) may strike one of the phosphor crystals on 
the surface of the tube. The phosphor will transmit this energy unaffected 
until the quantum reaches an "active center," where it starts a process 
similar to that by which the mercury atom was excited (by the impact of 
the electron) and releases a photon of visible radiation. (See Fig. 1-13.) 

Phosphors that may be excited to 
release visible radiation are coated 
on the inside of the fluorescent lamp 
in the form of a microcrystalline 
powder of exceptionally high chemi- 
cal purity. 

Less than 0.01 per cent of certain 
impurities in a phosphor may re- 

1 micron = 10.000 angstroms = 1/10,000 dllCe the lumen P er Watt ratin S ° f 

centimeters the lamp in which it is used by 20 

FIG. 1-13 Fluorescence curve of zinc- t y u percentages 

beryllium-silicate phosphor showing in- F J . \ ■ ■ , 

itial excitation by ultraviolet rays and of other "mtentional impurities 
subsequent release of visible radiation, called activators are usually required 

for efficiency. 
Figure 1-14, a simplified energy diagram for zinc sulphide, provides an 
explanation. To release radiation from a crystal of pure zinc sulphide, 
an electron resting at energy level A must be knocked up to excitation 
level D. Since it requires a great deal of energy to effect such a large 
transition, the process is inefficient at best and may never occur. 

Addition of a very small quantity of an activator (copper) results in the 
presence of electrons of the copper atoms at intermediate energy levels B 
and C. By comparison with those at level A , the activator electrons are 
relatively free to move about and since they are initially at a higher level, 
less energy is required to knock them up to level D. 



a 

z 


EXCITATION 


FLJUORESCENCE 


«uj 


(ABSORPTION) 


(RESPONSE) 


Z<0 


r\ 


/""N. 


°s 


l\ 


/ \ 


fO 


\ 


/ \ 


a.f> 


1 \ 


/ \ 




M 


/ © \ 


< 


/ , ,\ , i , > 


i i i i i^ i 



0.2 0.3 0.4 0.5 0.6 0.7 
WAVELENGTH IN MICRONS 



PHYSICS OF LIGHT PRODUCTION 



1-19 



The return of electrons from excitation level D to intermediate level C 
or B or A in small steps will result in the release of visible radiation. 

If the luminescent process continues only during the excitation it is 
called fluorescence. 



(5) POSSIBLE ENERGY LEVEL (EMPTY OF ELECTRONS UNDER STABLE CONDITIONS) 

==£^= 



o o o 

o o 
o 



°©° 

D O 

o o 
o® 



o o 

o o ~ o 



o o o 

°°" o Q 

' ° ° o ° I 

o o cc 



O O FILLED 

O. WITH 
O O ACTIVATOR ° 
~0 " ELECTRONS " 



O O 






o 



< o o 
5 o 

< o o _, o 

o o o 



O O O O ° 



o w o o 

o o _ o 

o ■ o ( 



°oo 
o o 



00 u o0 u o°o ^o u o uu T u o° 

(A) STABLE ELECTRON ENERGY LEVEL 
Oo q nOn°n°o O°o 0°0° O 



METASTABLE OR 
TRAPPING LEVELS 



- TRANSITIONS 
CAUSED BY 
THERMAL ENERGY 



EMPTY UNDER 
STABLE CONDITIONS 



» O o o C' 

. O 
OOO o 



OoOqO o °„oo 

)OO n u --' J - n " 
o o ° 



o 

I ( 
o o 



o o 

o 



°o°oo 



o o o 



WITH COPPER ACTIVATOR 



NO ACTIVATOR 



FIG. 1-14. Simplified energy diagram for copper-activated zinc sulphide phosphor. 

Some materials continue to emit light after the source of excitation 
energy has been removed. This phenomenon is called phosphorescence. 
It results from the transition of an electron from one of the metastable or 
trapping levels (Fig. 1-14) to which it may have been knocked during ex- 
citation from B or C, or in which it may have been stopped on its return 
from D. The release is effected by the thermal energy of the crystal. 

Effect of temperature. If the temperature of the crystal is maintained 
at a low value the electrons may be trapped for an indefinite period of time, 
finally being released when the costal is heated, minutes or even hours 
after excitation. 

Relationship between activation impurity and efficiency. Table 1-5 and 
Fig. 1-15 show the critical relationship which may exist between acti- 
vator, impurity, and efficiency in fluorescent lamps. 



Table 1-5. Effect on Fluorescent Lamp Efficiency of Small Quantities 
of Impurities in the Phosphor 4 



TEST LAMP* 


PER CENT IRON 


EFFICIENCY! 

(lumens per watt) 


1 
2 
3 

4 


0.001 
0.01 
0.10 
1.0 


62.0 
56.2 

48.7 
9.0 



* Coated with zinc silicate ZnO-SiOa + 1 per cent manganese contaminated with the indicated quanti- 
ties of iron impurities. 

t Neglecting ballast consumption. 



1-20 



I E S LIGHTING HANDBOOK 






20 

OX) I 0.02 0.04 O.I 0.2 0.4 I 2 4 I 

PER CENT MANGANESE 
IN2ZhO-Sl0 2 PHOSPHOR 

FIG. 1-15. Effeet of activator con- 
centration on fluorescence of zinc sil- 
icate. 



0.6 















/ 






CURRENT DENSITY 

MICROAMPERES 

PER SQ CM 








I — 








w 








- 












7% 


o/ 


























- 




















- 




















- 




















- 






















/ 


















- 




















- 


' \' 










i 




1 


1 



0.2 0.4 0.6 1.0 2 4 6 IC 

SCREEN POTENTIAL IN KILOVOLTS 



FIG. 1-16. The light output of zinc sul- 
phide is a function of screen potential and 
current density in a cathode-ray tube. 



Table 1-6 reveals the color effect of activator changes. Table 1-7 
includes the characteristic color of radiation emitted by several common 
phosphors. 

Stokes law, which states that the emitted radiation must be of longer 
wavelength than that absorbed, is based on two facts: 

1. Relatively large quanta (associated with short wavelengths) are 
required to raise electrons to the high excitation energy levels from which 
fluorescent and phosphorescent processes may begin. 

2. Transition of displaced electrons to their stable level usually occurs 
in several short steps giving rise to the smaller quanta associated with 
longer wavelengths. 

Note: Certain "anti-stokes" emitters exist which store energy in the 
metastable or trapping levels and will release wavelengths shorter than 
those required to excite them. 5 



Table 1-6. Effect of Activators on the Wavelength of Light Emitted by 

a Phosphor 



PHOSPHOR 

(per cent by weight) 



Zinc sulphide 

100 
90 
80 

75 



Cadmium sulphide 



1(1 

20 
25 



WAVELENGTH OF MAXIMUM FLUORES- 
CENCE 
(micron) 



Ictivator Silver 

0.4600 
.4740 
.4920 
.5030 



Copper 

0.5230 
.5400 
.5790 
.6100 



PHYSICS OF LIGHT PRODUCTION 



1-21 



Table 1-7. Color Characteristics of Several Inorganic Phosphors 







PEAK OF 




MATERIAL 


ACTIVATOR 


FLUORES- 
CENT BAND 
(micron) 


COLOR OF 
FLUORESCENCE 


Zinc silicate 


Manganese 


0.5280 


Green 


Zinc beryllium silicate 


Manganese 


.5925 


Yellow-white 


Cadmium borate 


Manganese 


.6150 


Pink 


Cadmium silicate 


Manganese 


.5950 


Yellow-Pink 


Magnesium tungstate 


None 


.4820 


Bluish-white 


Calcium tungstate 


None 


.4130 


Blue 


Calcium tungstate 


Lead 


.4420 


Blue 


Calcium phosphate 


Cerium 


.3600 


* 


Calcium phosphate 


Thallium 


.3325 


* 


Calcium phosphate 


Cerium and manganese 


.6500 


Red 



* Ultraviolet radiation. 



Miscellaneous Forms of Luminescence 

The electron excitation which results in the following luminescent 
processes is fundamentally the same as that which takes place in a fluores- 
cent lamp. 

Cathodoluminescence is the phenomenon observed when the screen of a 
cathode-ray tube such as that used in a television or radar receiver is bom- 
barded with high-voltage electrons. 

Figure 1-16 indicates the variation of light output for various conditions 
of voltage and current density. 

In an experimental television projection tube operating at 30,000 volts, 
a brightness of about 10,000 candles per square centime ter has been pro- 
duced with a beam intensity of 20 watts on a spot 0.5 square millimeter in 
area. It was accompanied by rapid deterioration of the phosphor. 

Certain chemical reactions proceeding at room temperature are accom- 
panied by the production of light. This is known as chemiluminescence. 
The oxidation of phosphorus in air and of pyrogallol in solution are familiar 
examples. 

A type known as bioluminescence occurs when luciferin, a substance 
synthesized by living cells, is oxidized in the presence of molecular oxj^gen 
and an enzyme, luciferase. 

The phosphorescence of sea water results from the presence of an enor- 
mous number of unicellular organisms which secrete luciferin and luciferase 
and oxidize when the disturbance of the water excites them. 

The firefly exhibits a similar ability. 

Triboluminescence is the term applied to light produced by friction or 
crushing. The phenomenon may be observed when pressure-adhesive 
tapes are unrolled or when lumps of cane sugar are rubbed together in a 
dark room. 



1-22 I E S LIGHTING HANDBOOK 

Natural Phenomena 

Sunlight. Energy of color temperature about 6,500 Kelvin is received 
from the sun at the outside of the earth's atmosphere at an average rate of 
about 0. 135 watt per square centimeter. About 75 per cent of this energy 
is transmitted to the earth's surface at sea level (equator) on a clear day. 

The apparent brightness of the sun is approximately 160,000 candles per 
square centimeter viewed from sea level. Illumination of the earth's 
surface by the sun may be as high as 10,000 footcandles; on cloud} 7 days the 
illumination drops to less than 1,000 footcandles. See Section 9. 

Sky light. A considerable amount of light is scattered in all directions 
by the earth's atmosphere. The investigations of Rayleigh first showed 
that this was a true scattering effect. On theoretical grounds the scatter- 
ing should vary inversely as the fourth power of the wavelength when the 
size of the scattering particles is small compared to the wavelength of 
light, 6 as in the case of the air molecules themselves. The blue color of a 
clear sky and the reddish appearance of the rising or setting sun are com- 
mon examples of this scattering effect. If the scattering particles are of 
appreciable size (the water droplets in a cloud, for example), scattering 
is essentially the same for all wavelengths. (Clouds appear white.) 

Polarization in parts of the sky may be 50 per cent complete. 

Moonlight. The moon shines purely by virtue of its ability to reflect 
sunlight. Since the reflectance of its surface is rather low, its brightness 
is approximately 1,170 footlamberts. 

Lightning. Lightning is a meteorological phenomenon arising from the 
accumulation in the formation of clouds, of tremendous electrical charges, 
usually positive, which are suddenly released in a spark type of discharge. 

The lightning spectrum corresponds closely with that of an ordinary 
spark in air, consisting principally of nitrogen bands, though hydrogen 
lines may sometimes appear owing to dissociation of water vapor. 

Aurora borealis (northern lights). These hazy horizontal patches or 
bands of greenish light on which white, pink, or red streamers sometimes 
are superposed appear between 60 and 120 miles above the earth. Appar- 
ently, they are caused by electron streams spiraling into the atmosphere, 
primarily at polar latitudes. Some of their spectrum lines have been 
identified with transitions from metastable states of oxygen and nitrogen 
atoms. 

REFERENCES 

1. Compton, A. H., "What is Light," Sci. Monthly, April, 1929. Condon, E. U., and Morse, P. M., Quantum 
Mechanics, McGraw-Hill Book Company, Inc., New York and London, 1929. Richtmyer, F. K., and Ken- 
nard, E. H., Introduction to Modern Physics, McGraw-Hill Book Company, Inc., New York and London, 
1942. Swan, W. F. G., "Contemporary Theories of Light," J. Optical Soc. Am., September, 1930. 

2. Maxwell, J. C, A Treatise on Electricity and Magnetism, Vol. 2, Clarendon Press, Oxford, 1904. 

3. Forsythe, W. E., Measurement of Radiant Energy, McGraw-Hill Book Company, Inc., New York and 
London, 1937. 

4. Marden, J. W., and Meister, George, "Effects of Impurities on Fluorescent Compounds," Ilium. Eng., 
May, 1939. 

5. O'Brien, B., "Development of Infra- Red Sensitive Phosphors," J . Optical Soc. Am., July, 1946. Paul, 
F. W., "Experiments on the Use of Infra-Red Sensitive Phosphors in Photography of the Spectrum," J. Opti- 
cal Soc. Am., March, 1946. 

6. Hulbert, E. O., "Brightness and Polarization of the Daylight Sky," J. Optical Soc. Am., March,1946. 

7. Goodeve, C. F., "Relative Luminosity in the Extreme Red," Proc. Roy. Soc. (London) A., Vol. 155, 
No. 886, 1936. 



SECTION 2 
LIGHT AND VISION 

Joint 'professional responsibility. Though the ophthalmologists and op- 
tometrists are responsible for the care of the eyes, their ultimate success 
in the discharge of this responsibilit}' - depends in part on the co-ordinated 
skills of the architect, decorator, and illuminating engineer. ) 

Effect of poor illumination. If forced to live or work under conditions 
of insufficient or poor quality illumination, or both, persons with normal 
eyes frequently experience temporary discomfort or disability that re- 
duces their visual efficiency. Over a period of time they have^been known 
to suffer semipermanent or permanent impairment of vision. 1 
I Benefits of good illumination are greatest for those with subnormal vision. 
Lacking light, the best eyes are useless. The vision of those persons whose 
visual deficiency the specialist is unable to correct or has not corrected to 
normal (through the prescription of proper training, or of lenses, medica- 
tion, or surgery) is more noticeably affected by the quantity and the qual- 
ity of illumination than is the vision of persons with normal or corrected 
to normal vision. 

For these reasons the illuminating engineer shares with the eye specialist 
the responsibility for providing the public with the means for achieving and 
maintaining the best vision attainable within the limits of engineering de- 
velopment and economic feasibility. Demonstrations of co-operation 
between practitioners in each field are becoming more common as it is 
realized that the objectives of the professions are the same. 

Industrial progress in sight conservation. The trend in industry is to- 
ward the assignment of vision problems, including those related to job 
analysis, to committees or boards comprising a medical director, a safety 
engineer, an ophthalmologist or optometrist, and an illuminating engineer. 2 

The American Standard Safety Code for the Protection of Heads, Eyes,and 
Respiratory Organs, published by the National Bureau of Standards, de- 
scribes the most common occupational eye hazards and means of prevent- 
ing eye injuries, and includes specifications for goggles designed to protect 
against glare, invisible radiation, fumes, and flying particles. 

Child development research. In Texas, where a long-range research into 
child development is being conducted, illuminating engineers and eye 
specialists are prominent in the interprofessional commission organized 
to guide the program. 3 

The Visual Process 

i The functions of the eye all depend on its ability to transform a light 
stimulus into an impulse that may be transmitted through the nerve fibers 
to the brain. There, the impulse is analyzed and a reaction initiated. 
The undistorted perception of contrast and color, of shape and depth, 
and of motion and direction, and therefore, most voluntary thought and 
action depend on the consistent response of the eye to light. / 

Note: References are listed at the end of each section. 

1 



2-2 I E S LIGHTING HANDBOOK 

Seeing skills must be learned and therefore are not uniformly developed 
in all individuals. Visual training in many instances is an un-co-ordinated 
and forgotten phase of instruction in some other skill, and may exist only 
in an unconscious trial and error process initiated during the development 
of a related dexterity (of the fingers, for example). There are notable ex- 
amples, however, of co-ordinated visual training. 

Several successful programs were conducted on a very large scale during 
World War II by the armed services. These prepared personnel for 
assignments (as lookouts, photo interpreters, and so on) requiring the 
highest possible development of certain visual skills. 

In industry, special visual equipment, instruction, and practice is re- 
quired in many operations, particularly in those involving inspection. 

Educators have found that slow readers may sometimes improve both 
speed and accuracy if given proper visual instruction. 

Psychological considerations introduced during the learning period may 
account, at least in part, for individual color preferences and the associa- 
tion of certain colors with temperature levels. 

The Structure of the Eye 

The structure of the eye is often compared with that of a camera, as 
in Fig. 2-1 A. 

- The iris is an opaque fibrous membrane resting against the crystalline 
lens. Reflexes in this membrane result in variations of the diameter (0.079 
to 0.315 inch) of its central aperture, the pupil. 

The attendant variations in area of the pupil (0.00465 to 0.0775 square 
inch) provide compensation by factors between 1 and 1G for wide variations 
in the brightness of the field of view. The pupil is similar in its function 
to the aperture stops in a camera. Compensation for the extremely wide 
range of brightness encountered in nature also involves the adaptation 
process. 

The ciliary muscles comprise the focusing mechanism of the eye. By 
controlling the curvature of the crystalline lens,- they change the focal 
length of the cornea-lens optical system to permit near vision. 

In the relaxed state, the lens (with an equivalent focal length of 0.59 
inch) forms on the fovea a sharp inverted image of objects at distances 
between 20 feet and infinity located along or close to its optical axis. An 
image about 0.03G inch high is formed of a man 100 feet away. 

To focus on near objects (closer than 20 feet) the muscles must be 
tensed. 

The retina comprises millions of light-sensitive nerve endings distributed 
throughout an almost transparent membrane about 0.0087 inch thick. 
An enlarged and simplified cross section of these nerve endings is shown in 
Fig. 2-lB. 

The light-sensitive nerve endings of the retina have their counterpart in 
tiny particles of photosensitive chemicals that give a photographic emul- 
sion its image preserving ability. The size and the distribution of these 



LIGHT AND VISION 



2-3 



nerve endings limit the resolving power or visual acuity of the eye in some- 
what the same manner that particle size and dispersion control the "graini- 
ness" of a photographic emulsion. They are attached individually or in 
groups to fibers of the optic nerve. 

There are two distinct types of nerve endings, known because of their 
shape as rods and cones. 



SYNAPSES CONES 



CORNEA 




APERTURE 
STOP-., 



OPTIC NERVE r -^ 

FIBERS BIPOLAR CELLS 



FIG. 2-1 A. Simplified vertical cross section of the human eye showing its camera- 
like structure. B. Magnified section of the retina simplified to show only the prin- 
cipal nerve structures. 

Cones approximately 0.000126 incrr in diameter found throughout the 
retina are concentrated in the fovea,' an oval-shaped mosaic (approxi- 
mately 0.0118 inch b} r 0.00945 inch along its axes). The cones of the fovea 
are connected individually to single fibers of the optic nerve. Best avail- 
able data suggest that the entire retina includes 6.3 to 6.8 X 10 6 cones. 4 

The section of the retina containing cones only includes the fovea and 
the area immediately surrounding the fovea; this section subtends a 1- 
to 2-degree angle which has its apex in the iris plane. 

Photopic (cone) vision exclusively is used for the discrimination of fine 
detail in critical seeing tasks and for the discrimination of color. The 
relative sensitivity curve of cones is given in Fig. 2-2. Because of their 
small diameter, close packing, and individual connections to the optic 
nerve, cones transmit a very sharp image showing considerable detail. 
Having low sensitivity they contribute little to the visual sensation when 
brightnesses in the field fall below 0.01 footlambert, as at night. 

Rods approximately 0.00197 inch in diameter are dispersed throughout 
the parafoveal retina in a lower concentration per unit area than of cones 
in the fovea. The concentration of rods continues to decrease as their 



2-4 



I E S LIGHTING HANDBOOK 



distance from the fovea is increased, and they are usually connected in 
groups to a single fiber of the optic nerve. Between 110 X 10 6 and 125 
X 10 6 rods have been counted in the retina. 4 

Scotopic {rod) vision begins to function when field brightnesses drop 
below 0.01 footlambert. The gray appearance (regardless of color) of 
objects under low illumination levels is one consequence. Because of the 
coarse rod reception mosaic and the multiple connections of rods to single 
nerve fibers, sharp images are not transmitted and objects appear as fuzzy 
silhouettes. The optical axis for rod vision is removed by 5 to 10 degrees 
from the fovea. As a result one usually sees best by somewhat averted 
vision at low brightness levels. 



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38 0.42 0.46 0.50 0.54 0.58 0.62 0.66 0.70 0.74 
WAVELENGTH IN MICRONS 




1 micron = 10,000 angstroms = 1/10,000 centimeter 

FIG. 2-2. Relative spectral sensitivity curves 
for photopic (cone) and scotopic (rod) vision show- 
ing the Purkinje effect on the wavelength of maxi- 



mg the Furkinj 
mum sensitivity 



FIG. 2-3. In the rods, both 
chemical and photochemical ac- 
tivity has been observed involv- 
ing rhodopsin, retinene, vitamin 
A, and protein. 



The macular pigment, a yellow layer covering the fovea and area immedi- 
ately surrounding it, is believed to be one cause of the difficulty of obtain- 
ing identical color matches from different observers. Since it varies in 
color between individuals and appears to deepen in color with age, the 
spectral composition of light that must pass through it before the cones 
are stimulated will be modified and thus modify any judgement passed 
by an observer making a color match. 

The Photochemical Theory 

Because of the complexity of the visual process, which includes many 
uncontrollable variables, a complete investigation of most visual phe- 
nomena is almost impossible at the present time. Nevertheless, sufficient 
experimental evidence has been collected to justify the general acceptance 
of the fundamental concepts of the photochemical theory of vision. 5 



LIGHT AND VISION 2-5 

The theory proposes that each neurone (rod or cone) contains a photo- 
sensitive substance S that forms upon exposure to light (among other 
things) a substance A. Also, there is a chemical reaction by which S is 
produced. Though the exact composition of the chemicals involved is not 
known, researches 6 support the belief that in the rods S is rhodopsin or 
visual purple, a rose-colored liquid; A is retinene, a yellow decomposition 
product; and vitamin A is an intermediate product in the chemical reac- 
tion. It appears that the relationship between these substances is as 
shown in Fig. 2-3. The speed of photochemical reactions between S and 
A is rapid as compared with that of the chemical process that includes 
production of vitamin A. 

Though it is believed similar reactions take place in the cones, the 
chemicals of the human cones have not been isolated. 

In an attempt to fit the theory to the available experimental data on 
dark adaptation, a modification has been proposed. 7 It includes five 
postulates: three expressions for the velocity of the reactions just de- 
scribed and two expressions for the frequency of electrical impulses by 
which visual stimuli are transmitted through the optic nerve to the brain. 8 
The modification has the advantage of generality over earlier forms of the 
theory that makes possible its application to the mathematical analysis 
of any visual phenomenon. Good correlation has been obtained with 
several experimental data but unexplained deviations from others have 
been noted. 

Color discrimination, though known to depend on the proper functioning 
of the cones, is not yet understood. 

It has been proposed that three types of photosensitive chemicals exist 
in the cones and that each has a distinct spectral absorption curve. 9 The 
existence of three types of nerve fibers, through which primary color 
stimuli may be transmitted as distinct impulses, has also been suggested. 10 

Though all colors appear gray at low illumination levels because of the 
deficiency of the rods, which provide no color perception, the relative 
brightnesses of different colored surfaces having the same reflectance or of 
sources emitting equal quantities of energy of different wavelengths will 
depend on the colors involved. In general, yellow-greens will appear 
brighter than reds or blues. Similar in shape to the curve for the cones, 
the peak of the rod sensitivity curve is displaced toward the shorter wave- 
lengths. (See Fig. 2-2.) This displacement, known as the Purkinje 
effect, occurs gradually as the observer adapts to low brightnesses and 
depends more upon the rods and less upon the cones. 

The adaptation of the eye to different brightness levels above 0.01 foot- 
lambert involves only the cones and is complete after 10 minutes of ex- 
posure to each new field. For most practical purposes the process ma} r be 
considered complete after 0.5 to 2 minutes of exposure. 

Dark adaptation is the term used to describe adaptation to levels below 
0.01 footlambert. In the transition region between 0.01 and 0.001 foot- 
lambert this will involve both rods and cones. Only rods are operative 
at levels below 0.001 footlambert. 



2-6 



I E S LIGHTING HANDBOOK 



The rate of adaptation is a function of the initial adaptation level and 
of the color to which the eye has been exposed. Initial exposure to high 
brightness levels of blue (short wavelength) radiation causes reduced 
rates of adaptation (greater total time). Though it has been found that 
the adaptation level may continue to decrease for several hours if the eyes 
are kept in darkness, for practical purposes the process may be considered 
complete after 30 minutes. 

Factors of Vision 

For evidence of the similarity of the objectives of the eye specialist and 
the illuminating engineer, it is only necessary to compare the criteria, 
i.e., the factors of vision, against which each group judges adequacy of 
illumination : 



ILLUMINATING ENGINEER 

Visual acuity 
Contrast 
Time or speed 
Brightness 



EYE SPECIALIST 

Visual acuity 
Visual efficiency 
Visual speed 
Visual comfort 
Visual health 




A 
3~- 



FIG. 2-4^4. Common visual acuity test objects showing detail (d) to be 
seen and the maximum angle subtended (.4). For normal vision rf m i n = 1 
minute. In most test objects A — 5d. 

Visual Acuity 

Visual acuity is the ability to distinguish fine detail. Eye specialists 
express it either as a ratio of the distance at which a given line of letters on 
a Snellen test chart can be seen by the observer being tested to the dis- 
tance at which an observer with normal vision could see it, or as a visual 
efficiency rating (expressed in percentages) related to the size of character 
in each line, if the American Medical Association chart is used. 

Most persons with apparently normal vision can distinguish the details of a 
black object on a white background if the detail subtends at least 1 minute at the eye. 

At an observation distance of 20 feet (arbitrarily selected as representative of 
distance vision) the characters in the normal lines of both charts (20/20 Snellen, 100 
per cent A.M. A.) subtend 5 minutes and their detail subtends 1 minute. Details 
in the 20/10 line subtend 1 minute at 10 feet and those in the 20/40 line subtend 1 
minute at 40 feet. Thus a person with Snellen rating of 20/40 sees at 20 feet what a 
normal observer would see at 40 feet. 



LIGHT AND VISION 



2-7 



100% 
95% 
90% 
85% 
80% 
75% 
70% 
65% 



55% 



50% 



45% 



A.M. A. TEST CHART 



30% 



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20/100 



20/200 



1 FIG. 2-4.B. Comparison of reduced size Snellen and A.M. A. visual acuity 
test charts. (The standard A.M. A. chart is printed on two aides of a single 
card.) 

Visual acuity is also expressed (by the research worker) as the reciprocal 
of the angle (minutes) which the smallest detail in a test object subtends 
at the eye. 

A laboratory acuity value of one means that the observer can just perceive a test 
object which subtends 1 minute at the eye; a value of two denotes that an 0.5 minute 
object can just be distinguished. 

Figure 2-4 shows three common test objects and the relationship between 
Snellen and A.M.A. lines and ratings. A uniform illumination of 10 foot- 
candles on the charts should be provided for routine examinations. 



2-8 



I E S LIGHTING HANDBOOK 



Visual acuity increases with the brightness of the task. The results of 
one study of the relationship are plotted in Fig. 2-5-4, which indicates that 
the rate of increase in visual acuity with increased brightness diminishes 
at high values of background brightness. The curve rapidly approaches a 
maximum at brightnesses greater than 10,000 footlamberts. 11 




A 



o.oi o.i i to 100 

BRIGHTNESS OF BACKGROUND 



1,000 10,000 100,000 
IN FOOTLAMBERTS 



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< 



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BRIGHTNESS OF SURROUND 

IN FOOTLAMBERTS 

B 



5 10 50 100 500 1,000 

BRIGHTNESS OF TEST OBJECT 
IN FOOTLAMBERTS 

c 



FIG. 2-5. Maximum acuity for any test object is attained when the surround 
brightness does not exceed that of the task, and is not less than one tenth that of the 
task. 

A. Variation of acuity with background brightness for a black test object on a 
white background. B. Variation of acuity with surround brightness for con- 
stant brightness test object (B t = 12.6 footlamberts). C. Acuity versus test object 
brightness for three values of surround brightness. 

The maximum achievable visual acuity is believed to be approximately 
2.46 (visual angle = 0.406 minute with the international test object). 12 
Ninety and 95 per cent maximum acuity may be attained at 150 footlam- 
berts and 1,300 footlamberts, respectively. To attain more than 95 per 
cent maximum acuity, the brightness required is more than 1,300 foot- 
lamberts (as in nature). Maximum acuity may be obtained only when the 
surrounding brightness does not exceed that of the task and is not less 
than one tenth that of the task. (See Fig. 2-55 and Table 2-1, pg. 2-12.) 



LIGHT AND VISION 



2-9 



Contrast 

If an object is to stand out against a background, there must be contrast 
between the two. Contrast is the difference in brightness between the object 
and its background divided by the brightness of the background: 

B\ — Bi 



C = 



where 



C 
B 1 

B 2 



Bi 

= contrast 
= brightness 
lamberts) 
= brightness 



of background (foot- 
of object (footlamberts) 



since brightness, B, equals illumination, E, X reflectance p 

„ _ Epi — Epi _ Pi — pi 
Ep\ P\ 

where E = illumination (footcandles) 

p = reflectance (perfectly diffuse surface 
only) 
The effects of contrast may be divided into two classes: 

(1) contrasts of small objects against their background, and 

(2) contrasts between large contiguous surfaces. 

The first involves the variation of contrast with size, as well as with 
illumination. In the second, size is not a factor. 

Small objects vs. background. The relationships between acuity, con- 
trast, and brightness for the range of brightness between 0.0001 and 100 
footlamberts are shown in Figs. 2-6^1 and 2-65. 




O.OOOl 0.001 0.01 0.1 1 10 100 

BRIGHTNESS OF TASK BACKGROUND IN FOOTLAMBERTS 

FIG. 2-6. Relationships between contrast, brightness, and acuity. A. Re- 
lationship between contrast and brightness for threshold visibility (constant exposure 
time). B. Acuity attainable for various values of brightness with objects of 
different contrasts. 13 - M 



2-10 



I E S LIGHTING HANDBOOK 



Large contiguous surfaces. The minimum perceptible contrast between 
a background and a large contiguous surface: 



v^ min — 



£1 



is not easy to determine accurately by experiment since the fovea becomes 
adapted very rapidly to changing brightness. If the time of exposure is 
not carefully regulated, the result is not the minimum perceptible contrast 
but a value related to an adaptive brightness between the brightness of 
the background and that of the test area. Figure 2-7 shows minimum per- 
ceptible contrast and contrast sensitivity for various values of background 
brightness. 

Contrast sensitivity (1/C mt „) is similar in concept to visual acuity. It 
is a measure of the ability to discriminate slight contrasts. Ninety- 
five per cent of maximum contrast sensitivity may be obtained with 
a brightness of 90 footlamberts. Ninety per cent is obtained with 20 
footlamberts. 



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FIG. 2-7. Minimum perceptible contrast and contrast sensitivity versus 
background brightness. 



Speed of Vision 

It takes time to see. Speed of vision is a function of task brightness 
as shown by Fig. 2-8A. Considering the difference of test objects and 
observers, these data agree very well with results of later work on inter- 
national test objects, as plotted in Fig. 2-8(7. 

In reading a steel vernier rule, the speed of making the complete reading 
(tenth inch numbers, quarter divisions within the tenth, and exact position 
of the 25 part vernier) varies, as shown in Fig. 2-9-4, with the brightness 
of the highlight on the background of the rule against which the black 
divisions appear in bold relief. 16 



LIGHT AND VISION 



2-11 















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5 10 50 100 1 5 10 50 100 

u. BRIGHTNESS IN FOOTLAMBERTS ILLUMINATION IN FOOTCANDLES 
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REFLECTANCE OF 
BACKGROUND 
IN PER CENT= ^ 
























& 
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10 50 100 1 5 10 50 100 

ILLUMINATION IN FOOTCANDLES 
C 

FIG. 2-8. Speed of vision vs. size, contrast, and illumi- 
nation of the task. A . (I) Speed of noting the presence of 
2.43 minute black dot. (77) Speed of noting the orienta- 
tion of 1.82minute parallel bar test object. 14 ' 15 B. Speed 
of noting orientation of various sizes of black (p = 3 
per cent) on white (p = 78 per cent) parallel bar test 
object. C. Speed of reporting orientation of black (p = 4 
per cent) international test objects (right, 1 minute and 
left, 2 minutes) viewed against various backgrounds. 15 

Figures 2-95 and 2-9C show speed of vision variations for other tasks. 16 - 17 

Brightness 

Because it is the brightness of a surface rather than the illumination 
(footcandles) it intercepts which is utilized in seeing, misapplications may 
occur when footcandle levels recommended by the illuminating engineer 
for high reflectance surfaces are applied to dark surfaces, 



2-12 



I E S LIGHTING HANDBOOK 



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BRIGHTNESS IN 
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ILLUMINATION IN 
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1 2 3 4 5 6 7 8 9 10 20 30 40 

BRIGHTNESS IN FOOTLAMBE"RTS 

FIG. 2-9A. Speed of reading steel vernier rule vs. 
brightness of highlight surrounding black divisions. 16 
(Reading requires perception of 1/1000 inch deviation 
from alignment of divisions.) _ B. Speed of discriminat- 
ing brass and steel test objects against contrasting 
backgrounds. 16 C. Speed of reading vs. illumination 
(black Old English type on: A, white (p = 80 per cent) 
background; B, gray (p = 23 per cent) background. 17 



Table 2-1. Relationship between Brightness Visual Acuity and Contrast 

Sensitivity 



BRIGHTNESS REQUIRED 


MAXIMUM POSSIBLE ATTAIN- 
MENT UNDER IDEAL CONDITIONS 


Visual Acuity* 


Contrast Sensitivity 


(per cent) 


1,300 footlamberts 
150 footlamberts 


90 footlamberts 
20 footlamberts 


95 
90 



Black test object on white background. 



LIGHT AND VISION 



2-13 



The brightness in footlamberts of any nonspecular surface equals the in- 
cident illumination (footcandles) times the reflectance. Under the same 
illumination, the brightness of white paper (reflectance 80 per cent) will 
be four times that of cast iron (reflectance 20 per cent). 

Visual acuity, contrast sensitivity, and time vary directly and largely log- 
arithmically with brightness. Table 2-1 represents the best information 
presently available on the relationship between brightness, visual acuity, 
and contrast sensitivity. The effect of time is shown in Figs. 2-8 and 2-9. 

British Interior-Lighting Code 

The British (I. E. S.) code of interior lighting includes recommended 
illumination levels. These levels are estimated, on the basis of laboratory 
tests and standard test objects, to be sufficient to permit attainment of 
visual task performance rates equivalent to 90 per cent of their individual 
capacities by most persons with normal or corrected-to-normal vision. 



SIZE 
CRITICAL DETAIL 
OF SEEING TASK 



RECOMMENDED 
FOOTCANDLES 




FIG. 2-10. Scale A gives recommended 
illumination values (British practice) for 
high contrasting backgrounds. 16 Scale 
B gives recommended values for average 
contrast tasks. Scale C gives recom- 
mended values for low contrast tasks such 
as sewing with black thread on dark cloth. 
The following values of the ratio D/S 
(usual viewing distance D -4- dimension of 
detail S) correspond to the steps on the 
size scale: 

r4, 100-3, 200-1 r-3,200-2,450-1 r2, 450-1 ,900"| 
L minute J Lvery small J L small J 
r 1,900-1,500-1 r 1,500-1, 150-1 r 1,150-850"] 
L fairly small J L ordinary J L large J' 

One step higher on the foot-candle scale 
is recommended (British practice) when 
the objects are in motion and two steps 
if the task is also of long duration. The 
relative sizes of type suggest the type of 

installation: 10 — General lighting, 100 
General or general plus local lighting, 1000— 
Local supplementing general lighting. 



A / B \ C 

GOOD/AVERAGE\ poor 
•CONTRAST- 



Figure 2-10, taken directly from the British code, was developed from 
laboratory data of the type shown in Fig. 2-11. These were obtained from 
standardized performance tests (location of the gap in an international 
test object, black on white) conducted in laboratory cubicles under ideal 
conditions. 18 



2-14 



I E S LIGHTING HANDBOOK 



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FIG. 2-11. The relationship between visual performance (discrimination of black 
j nternational test objects on white) and illumination. 18 




FIG. 2-12. Nomograph de- 
signed to !give footcandles re- 
quired for 98 per cent perform- 
ance (British criterion) when 
the size of detail and reflectance 
of object and background are 
known. 



To obtain the footcandles recommended by the British for a percentage 
perfomance between 90 and 100, for object-background contrasts less 
than 100 per cent, multiply the 100-per-cent contrast value for the per- 
centage performance in question by where pi is the reflectance of 

Pi — P2, 
the background and p2 is the reflectance of the object or detail. The 
results are accurate in the 95 to 100 per cent performance range and 
are approximately true for performance a^-low as 90 per cent. 



LIGHT AND VISION 



2-15 



Using Fig. 2-12 the footcandles required for 98 per cent performance 
may be obtained: 

First, measure the critical size of the detail to be seen, the distance from the eyes, 
and the reflectance of the detail and its background. Then by plotting these values 
on the nomogram and drawing straight lines point to point (left to right), the foot- 
candles required are found. 

These values represent 98 per cent of maximum performance by un- 
fatigued, young observers with normal or corrected-to-normal eyes, by 
maximum exertion, in ideally lighted cubicles, free from any hindering 
influences. It is good engineering practice to provide a safety factor, 
especially when it is expedient to depart from the ideal test conditions of 
the laboratory. 

Note: For equal acuity the eyes of people around 60 years old (though 
normal for that age) require about twice the illumination required by the 
eyes of 20-year-olds. (See Fig. 2-13.) The handicap of persons with 
visual deficiencies decreases as the illumination is increased. 




FIG. 2-13. Because of the reduction in pupil size 
which accompanies advancing age, higher bright- 
nesses are required for equivalent effect in eyes of 
older observers. B x = brightness at x years as 
compared with brightness (B 2 o) at 20 years. 



30 40 50 60 70 
AGE IN YEARS 



Recommended American Interior-Lighting Practices 

Judged against the British criteria, current American practice 19 appears 
to permit achievement of a better performance rating than might be ex- 
pected under the British code. 

Visibility based upon size, contrast, and brightness. As a means of meas- 
uring visibility it has been proposed that the visibility of a series of twenty 
standard black-on-white parallel-bar test objects (Fig. 2-4A), each of which 
subtends a visual angle in the series 1, 2, 3,-20 minutes, be reduced to 
threshold by means of a graduated density neutral filter. 20 The density 
necessary to reduce each test object to threshold is assumed to represent 
the relative visibility of that object above threshold. 

A visibility meter operating on this principle is available. (See Fig. 
2-144.) Two identical filters, one for each eye, are provided in this 



2-16 



I E S LIGHTING HANDBOOK 



visibility meter. Both filters are calibrated, one in numbers (1-20) repre- 
senting the size (minutes) of the test object reduced to threshold during 
calibration by each setting of the filter, and the other in recommended 
footcandles. 

The footcandle scale is calibrated arbitrarily on the assumption that 10 
footcandles is a conservative illumination for reading 8-point (3.7 minute 
size) black Bodoni type on white paper. For normal eyes the visibility of 
this reading task under 10 footcandles is chosen as a conservative standard 
by the designers. The user of the meter may, if he wishes, choose another 
standard (20 footcandles for example) and multiply scale readings by the 
new standard divided by 10 (scale reading X 20/10). 




6 

? 5 

UJ 

Q 3 



LUCKIESH-MOSS 
\ VISIBILITY METER 
\ 100% CONTRAST 

V 


















\ 












\ 












\ 




98% PERFORMANCE 
(BRITISH CRITERIA) 
SIZE, CONTRAST, 
y" TIME AND 
^ BRIGHTNESS 


















^^ 


s 
















-v 



I 5 10 50 100 1000 

ILLUMINATION IN FOOTCANDLES 



FIG. 2-14A. Luckiesh-Moss visibility meter showing graduated density filters. 
B. Comparison of footcandle recommendations obtained from a nomograph (Fig. 
2-12) and by means of the Luckiesh-Moss visibility meter. 



When the background brightness equals that used in calibrating the 
meter (usually 8 footlamberts) the observer by adjusting the filters so that 
the visibility of a new task is reduced to threshold may equate the task 
visibility to that of a standard test object under the recommended value 
of illumination. In Fig. 2-145 the footcandles required for the 98 per 
cent performance obtained using the nomogram (Fig. 2-12) are compared 
with the footcandles obtained with this visibility meter. 



LIGHT AND VISION 



2-17 



Age and Subnormal Vision 

There is a general degeneration of bodily functions with age. The re- 
duction in visual acuity is shown by Fig. 2-15. Pupil size decreases with 
age as shown in Table 2-2. 



Table 2-2. Diameter of the Pupil in Millimeters 22 



AGE 


IN DAYLIGHT 


AT NIGHT 


DIFFERENCE 


20 


4.7 


8.0 


3.3 


30 


4.3 


7.0 


2.7 


40 


3.9 


6.0 


2.1 


50 


3.5 


5.0 


1.5 


60 


3.1 


4.1 


1.0 


70 


2.7 


3.2 


0.5 


80 


2.3 


2.5 


0.2 



The Stiles-Crawford effect is the reduced effectiveness of the rays of 
light entering the pupil at increasing distances from the center. The 
effect is not strong enough, however, to compensate for the reduction in 
pupil size with age, which makes it necessary to increase brightness (Fig. 
2-13) if the same acuity, minimum perceptible contrast, and speed are to 
be maintained as an observer's age increases. 23 

Accommodation is the adjustment of the focal length of the eye for view- 
ing objects at different distances. Upon tensing of the ciliary muscles, 
the lens bulges (Fig. 2-16,4) to the proper contour to focus upon near 
objects. 

The youthful eye tends to be flexible and therefore can focus upon very 
close objects (at eight years to 3 inches or less). 

Age tends to stiffen the lens capsule in its flattened shape to the extent 
that the muscles are no longer able to give it the convex contour necessary 
for close vision. (See Fig. 2-16.B.) 

An emmetrope is a person with normal 
vision. Presbyopia is the term applied 
to loss of accommodation. A myope is 
one who is near sighted and cannot accom- 
modate for far vision without correction. 

The amplitude of accommodation for 
these types of vision is improved by an 
increase of illumination on the task. (See 
Fig. 2-1QB.) The percentage of improve- 
ment is greatest for the presbyopes, and 
they also benefit much more in percent- 
age gain of visual acuity. (See Fig. 
2-165.) 



< 60 



< 20 



40 60 

AGE IN YEARS 



FIG. 2-15. The reduction of visual 
acuity with age. 21 



2-18 



I E S LIGHTING HANDBOOK 



SINUS 
VENOSUS 




OI40 



^ 100 



O 80 

z 



RELAXED FOR I ACCOMMODATED 
DISTANT VISiON FOR NEAR VISION 



PRESBYOPES 

NON-PRESBYOPES 




















A.L. AGE 63^ 
















J.B. AGE 42> 






































/k. 












^^E.L.AGE27 




X jf 


"s& 






y^~ 


V M.F. AGE 27 
3.S. AGE 53 


£e£^' - " — 


1 


1 


1 




I 


1 


I 


1 




10 20 30 40 50 60 70 
AGE IN YEARS 



5 10 50 100 

ILLUMINATION IN 



I 5 10 

FOOTCANDLES 



FIG. 2-16A. To adjust the curvature of the lens for focusing on near objects, the 
ciliary muscles are tensed, causing the lens to bulge. As the lens capsule stiffens 
with age the amplitude of this accommodation decreases as indicated by Duane's 
curves of norms of accommodation. B. Improvement in accommodation and acuity 
with illumination is greater for presbyopes than for emmetropes or myopes. 



Glare 



\ 



I Everyone has experienced visual sensations caused by brightness re- 
lationships in the field of view. If the conditions interfere with vision, a 
layman may describe the phenomenon objectively as veiling or perhaps as 
blinding glare. If the sensation is strong and unpleasant, he may use the 
subjective terms uncomfortable, annoying, or intolerable. / 

Because visual efficiency and comfort are the prime objectives of all 
utilitarian and of many decorative lighting designs, glare which interferes 
with seeing or causes discomfort is a serious defect. Glare is avoided or 
eliminated whenever possible. Although much has been said which might 



LIGHT AND VISION 2-19 

leacirUne to believe that there is an important difference between direct 
and reflected glare, if the results are evaluated in terms of the brightness 
viewed by the observer, it is not necessary to state whether the brightness 
is/of a glare source viewed directly or of its reflected image. 
J 'Although it may often be possible to modify a lighting design so as to 
eliminate glare, even after the design has been carried out in a practical 
installation, usually it is simpler and less expensive to avoid the defect 
in the original design. For this reason illuminating engineers are working 
to develop satisfactory preinstallation methods of evaluating design bright- 
ness relationships with respect to their potential glare effect. 

However, glare involves physiological and psychological as well as phys- 
ical factors, and to determine the true relationship between the many 
variables under all practical conditions is a formidable task. 

Despite the fact that a completely satisfactory solution is not in sight, 
several useful theories having individual merit have been proposed. How- 
ever, because each of the theories is subject to some justifiable criticism, 
glare is considered a controversial subject and the theories should be 
applied carefully. 

Though the desirability of judging glare phenomena against disability 
and discomfort criteria (distinct and unrelated in concept) has been agreed 
upon, and the utility of the Holladay-Stiles formula for evaluating dis- 
ability glare has been recognized, no similar agreement has been reached 
on a method of evaluating discomfort glare. 

The following convenient definitions, though not standard, serve to 
increase the precision achievable in glare discussions. Unless otherwise 
qualified the intended meaning in this handbook is that defined. 

Adaptation level (B A ) — that brightness of a perfectly uniform field which 
would result in the same state of adaptation as the practical field of view 
in question. 

Task (t) — the 2-degree area imaged on the fovea which includes the 
object or detail to be seen and the contrasting background. 

Surround (s) — all of the field of view not occupied by the task. 

Field of view (J) — comprises two monocular fields represented by two 
solid angles approximately 90 degrees wide and 120 degrees high that com- 
bine to form an approximately circular binocular field subtending about 
120 degrees. (See Fig. 2-21, pg. 2-26.) 

Glare source (g) — any brightness in the field of view which causes either 
visual disability or a sensation of discomfort. 

Disability Glare 

Disability-glare sources, by increasing an observer's adaptation level, 
reduce his contrast sensitivity or the contrast between a visual task and its 
background, or both. The same effect is observed if .a veiling brightness 
is superposed uniformly on a task and background, 24 



2-20 I E S LIGHTING HANDBOOK 

Case 1: Uniform Field — Task Brightness Equals Surround Brightness. 
Disability glare is present whenever a source of higher brightness than that 
of the task is superposed on the surround. The observer's initial adaptation 
level equals the task brightness, and his new adaptation level (glare effect 
included) equals the sum of the original level and the equivalent veiling 
brightness. 

The value of the equivalent veiling brightness for one or more glare 
sources (B g > B t ) may be obtained from the following equation: 

EVB = ~ir + -^r + -ir 

(See references 24 and 32.) 

where EVB = veiling brightness equivalent in effect to 

one or more glare sources (footlamberts) 
Ei, E2, E n — illumination on a plane through the ob- 
server's eye (_L line of sight) contributed 
by each glare source (footcandles) 
0i, 02, n — angle between the line from each glare 
source to the task and the observer's line of 
sight (degrees) 

The observer's new adaptation level (glare effect included) is: 

B A = B a + EVB (Holladay-Stiles formula) 26 
where B a — the observer's initial adaptation level (glare effect 

neglected) = the task brightness B t . 

It appears that foveal adaptation for a uniform field is 90 per cent de- 
pendent on the brightness of the portion of the field imaged on the fovea, 
the surround contributing only 10 per cent of the total effect. 25 (See Fig. 
2-18, K = 0.) 

Case 2: Nonuniform Field — Task Brightness Greater than Surround Bright- 
ness. Disability glare is present whenever the observer's new adaptation level 
Ba (glare effect included) is greater than task brightness B t . However, 
when the task is brighter than the surround, potential glare sources (B g > 
B,) may sometimes be superposed on the surround without causing dis- 
ability glare. 

The initial adaptation level B a (potential glare effect neglected) may be 
determined by direct measurement or by computation. 25 It is a function 
of task brightness B t and surround brightness B s and perhaps also of a 
brightness B n superposed on the surround. It will equal the contribu- 
tions of the several field brightnesses integrated with respect to the angles 
by which their positions are displaced from the line of sight. 25 

To determine if disability glare is present, the equivalent veiling bright- 
ness may be found by using the equation: 

10tt#i 10ttE 2 10wE n 
EVB = —j- + —3- + —*- 



LIGHT AND VISION 



2-21 



Then the new adaptation level is: 

B A = B a + EVB 

and disability glare exists whenever B A > B t . 

For the special situation shown in Fig. 2-17 in which the task is cen- 
tered on a surround of 115 degrees diameter and brightness B s on which is 
superposed a concentric annular area of brightness B Sl such that B s + B Sl 
= B t , and of variable outside radius 9, curves of B A /B t versus are plotted 
in Fig. 2-18 for several values of B s /B t . 



FIELD OF 
VIEW "X 




FIG. 2-17. One and one half degree 
task (brightness B t ) viewed against 
115-degree surround (brightness B 3 ) 
on which is superposed an annular area 
(O.D. = 2 0, I.D. = 1.5°) of bright- 
ness B Sl = Bt — B s . The variation 
adaptation brightness .„ ,r> -, - t i 

task brightness 
variation in 6 is shown in Fig. 2-18. 



Ba 

Bt 



H 


= B S /B t = 

^10 
















^5 


















^5 


















__3 
2 

1 
















I 


_ . 


1 


1 


1 


1 




I 


1 



0.8 I 2 4 6 8 10 20 40 60 

IN DEGREES 

FIG. 2-18. Variation in the ratio (adap 
tation brightness, B a /task brightness, B t ) 
with changes in angle for several values 
of k (equals surround brightness, Z? s /task 
brightness, B t ) in the field shown in Fig. 
2-17. 



The magnitude of the disability-glare effect on contrast sensitivity may 
be determined for any situation as follows : 

1. From Fig. 2-7 obtain the minimum perceptible contrast corresponding 
to the value of Ba. 

2. Substitute the minimum perceptible contrast in the equation for 
C m i n on page 2-9. 

3. Solve for (B 2 - B 2 ), (B x = B A ). 



4. The contrast sensitivity under glare condition will equal 



B a 



(Bi - B 2 ) 

It has been found convenient to express the relationship between B A and 
B t as a surround factor: 



A = 



Ba 
Bt 



2-22 



I E S LIGHTING HANDBOOK 




A 0.88' TEST OBJECT 
□ 1.17' " " 

O 1.76' " " 

• 3.95' & 3.20' " 
X 16.00' " 

E G =5FT-C THROUGHOUT 
(COBB 8. MOSS DATA) 



2.5 3 4 

SURROUND FACTOR A 



FIG. 2-19. Variation in contrast sensitivity with changes in surround factor (A = 
B A /B t ) for several sizes of test objects. 

Relative contrast sensitivity for various surround factors is plotted for 
several test objects in Fig. 2-19. 

Discomfort Glare 

The sensation experienced by an observer when brightness relationships 
in the field of view cause discomfort but do not necessarily interfere with 
seeing is known as the discomfort-glare effect. . . 

Lacking a standardized procedure for evaluating this effect, five con- 
temporary theories are presented; each has merit and in composite they 
represent the state of the art.^ With care and with an understanding of 
their individual limitations an experienced engineer may apply these theo- 
ries advantageously to the solution of practical problems. 

1. Shock concept. It is known that discomfort may be experienced 
when an observer adapted to one brightness level suddenly encounters 
the higher brightness of a potential-glare source. 

It has been proposed 26 that the following empirical formula be used to 
determine the maximum brightness of a potential-glare source which may 
be viewed suddenly without discomfort: 



where 



B g = 

K = 
B a = 



KB° a 3 



maximum comfortable brightness of 

a potential glare source (footlam- 

berts) 

75.4 (sometimes called the index of 

comfort) 

initial brightness level to which the 

observer was adapted immediately 

prior to encountering the potential 

glare source (footlamberts) 



LIGHT AND VISION 



2-23 



Table 2-3. 



co = solid angle subtended by the poten- 
tial-glare source, which is assumed 
to be the circular area centered on 
the axis of fixation (steradians) 

Comfort-Discomfort Threshold Brightness of Various 
Common Luminaires in Different Rooms 





LAMP 


BRIGHT- 
NESS 

OF 
LUMI- 
NAIRE 
(ft-L) 


SIZE OF ROOM IN FEET, NUMBER OF LUMINAIRES, 
HEIGHT OF LUMINAIRE 


LUMINAIRE 


12 x 12 x 8 
One 

6.5 feet 


30 x 30 x 12 
Nine 
10 feet 


SO x SO x 12 

Twenty-five 

10 feet 




Illumi- 
nation 
Level 
(ft-c*) 


Thres- 
hold 
Bright- 
ness 

(ft-L) 


Illumi- 
nation 
Level 
(ft-c*) 


Thres- 
hold 

Bright- 
ness 
(ft-L) 


Illumi- 
nation 
Level 
(ft-c*) 


Thres- 
hold 

Bright- 
ness 
(ft-L) 



FILAMENT-LAMP LUMINAIRES 



12" Diffusing sphere 


150- watt 


750 


7.3 


315 


12.8 


570 


14.8 


570 


14" 


200 


785 


10.2 


325 


18.2 


590 


21.0 


595 


16" 


300 


955 


15.9 


355 


29.0 


640 


33.6 


645 


18" 


500 


1280 


27.8 


400 


49.1 


715 


57.0 


730 


14" Semi-indirect 


200 


370 


8.0 


315 


14.7 


570 


17.0 


600 


16" " 


300 


455 


13.2 


345 


23.4 


625 


27.2 


650 


IS" " 


500 


610 


23.0 


390 


39.6 


690 


46.0 


715 


16" Luminous indirect 


200 


180 


7.0 


285 


12.8 


535 


15.7 


540 


18" 


300 


225 


11.2 


310 


20.4 


545 


25 


590 


18" 


500 


380 


19.0 


360 


34.5 


630 


42.3 


685 


20" 


750 


445 


27.5 


390 


50.1 


670 


61.4 


740 


20" 


1000 


645 


39.9 


435 


72.5 


740 


89 


825 



FLUORESCENT-LAMP LUMINAIRES 



10" x 4' Half cyl 
Diffusing 

12" x 4' Half cyl 
Diffusing 

14" x 4' Half cyl 
Diffusing 

10" x 4' Half cyl 
Semi-indirect 

,12" x 4' Half cyl 
Semi-indirect 

14" x 4' Half cyl 
Semi-indirect 



two 40-watt 
four 40 

two 40 
four 40 

two 40 
four 40 

two 40 
four 40 

two 40 
four 40 

two 40 
four 40 



220 
440 


9.6 
19.2 


290 
360 


16.4 
32.8 


490 
610 


18.9 
37.8 


185 
370 


9.6 
19.2 


275 
345 


16.4 
32.8 


470 
590 


18.9 
37.8 


160 
320 


9.6 
19.2 


270 
335 


16.4 
32.8 


455 

570 


18.9 
37.8 


115 
230 


8.7 
17.5 


280 
350 


15.3 
30.7 


475 
590 


17.7 
35.4 


95 
190 


8.7 
17.5 


270 
335 


15.3 
30.7 


455 
565 


17.7 
35.4 


80 
160 


8.7 
17.5 


260 
325 


15.3 
30.7 


440 
540 


17.7 
35.4 



495 
620 



475 
595 



455 
570 



485 
610 



460 
5S0 



445 

560 



*ft-c = footcandles on work of about 80 per cent diffuse reflectance. _ These footcandle values must be 
multiplied by 10 if the work has a diffuse reflectance of 8 per cent, by 4 if the work has a diffuse reflectance 
of 20 per cent, and so on. 



When the brightness of the potential glare source is known its value 
may be substituted for B g and the formula solved for K, the index of com- 
fort. Values of B g which result in values of K greater than 75.4 cause 
discomfort which becomes "intolerable" when K — 377; the smaller the 
value of K below 75.4, the smaller the probability that encountering the 
potential-glare source will cause discomfort. Since a shock is the cause, 



2-24 I E S LIGHTING HANDBOOK 

it is conceivable that the sensation may be of short duration. The exact 
duration will be determined in each case by the complex relationship of 
the variables in the adaptation process. 

Since it has been suggested that a series of discomfort shocks may have a 
cumulative fatigue effect (though each may seem instantaneous and of 
little consequence), it is believed desirable to apply a safety factor of 0.5 
to threshold values. Threshold values (no safety factor, K = 75.4) for 
several types and numbers of sources in typical rooms are tabulated in 
Table 2-3. In preparing Table 2-3, methods of evaluating the contribu- 
tions to the glare effect of all sources in the field, in addition to that fixated, 
were applied. 27 

2. Glare ratings. The following method of rating a lighting plan or in- 
stallation with respect to its direct-discomfort-glare effect has been pro- 
posed. 23 

The basic assumptions are as follows: 
First, the line of sight of the observer is horizontal. 
Second, the unit of discomfort is the effect produced by a glare source 
with the following characteristics: 

Area = 1 square inch 
Location = 10 feet from the eye, 10 degrees 
above the line of sight 
Brightness = 1,000 footlamberts, when the sur- 
round brightness against which it 
is viewed equals 10 footlamberts. 
The glare factor for a single potential glare source is determined by the 
following empirical formula: 



K 



A B 2 

D 2 2 S°- 6 
P 



5AD 2 2 S™ 

where K = glare factor for single source 

A = apparent area of source (square inches) 

r, , . , . e / footlamberts \ 

B = brightness or source I ) 

6 V 1,000 / 

D = distance from source to eye ( — ] 

\ 10/ 

= angle between horizontal and line above 

., , , /degrees\ 

it from eye to source I — =- — ) 

v io y 

c< , , . , , /footlamberts^ 

o = surround brightness I - 



10 

I = intensity of source in direction of the 
eye (candlepowcr) 

If there are numbers of potential-glare sources in the field of view, a 



LIGHT AND VISION 



2-25 



composite-glare rating may be obtained by adding together the factor for 
each individual source. 

In offices, drafting rooms, school rooms, and similar locations glare 
ratings of less than 15 are considered to indicate comfort on the basis of the 
exponents used in the equation. In factories, stores, and so on it is con- 
sidered that a higher glare rating may be permissible. 

3. Photochemical theory applied to brightness ratios. It has been pro- 
posed that discomfort glare be evaluated on a scale of comfortable bright- 
ness ratios derived from a modified photochemical theory of vision. 7 ' 29 



°8 

2C 



-\ 






























- >s 












s^BY GLARE SOURCE, U), 
^•v. IN STERADIANS: 






- v 
















n> 




















icr 5 






























io- 4 










- 






























- 






























- 




















I0" 3 
00 










- 






























i 


i 


i 


i 




l 


1 


1 


1 




i 


i 


i 


i 



20 40 60 100 200 400 1,000 
B A IN FOOTLAMBERTS 



4,000 10,000 



FIG. 2-20. Maximum comfortable brightness ratios 
(B g m! ,x/i?a) for various adaptation levels, B a , and sizes 
of glare source, w. 

In Fig. 2-20 are plotted comfort threshold brightness ratio curves ob- 
tained by substituting different values of B a and to in the following equa- 
tion: 

Bg^ = (B/Ba) co [000874 + y'-p 
B a CO 

where #<? max — maximum comfortable brightness of potential 

glare source (footlamberts) 
B a = observer's initial adaptation level (foot- 
lamberts) 
(B/B a ) oo = comfortable brightness ratio for a very 
large source 
co = solid angle subtended by potential glare 
source (steradians) 

To determine if a potential glare source will cause discomfort, find the 
adaptation level B a , the brightness of the potential glare source B g , and 
the solid angle co subtended by the source. 

All values of B g /B a which fall below a horizontal line through the inter- 
section of the B a ordinate and the proper co value curve will be comfortable, 
all those above will cause discomfort. 



2-26 



I E S LIGHTING HANDBOOK 



4. Evolution and glair. Evidence supports the belief that human eyes 
have developed through the ages to satisfy the needs of the natural human 
environment. Results of recent research indicate that man's normal 
habitat, based on the probability of his survival in the natural state (no 
clothes or shelter), is limited to the zone of the earth's surface covered by 
a 70-degree-Fahrenheit isotherm. 

On the assumption that the eyes have been prepared through the evolu- 
tionary process to function properly under the conditions of this zone, 
comfortable flux ratios characteristic of the zone have been studied for 
guidance in interior-lighting design. 

Based on an analysis of these data, Fig. 2-21 has been developed to sug- 
gest the comfortable limits of flux distribution ratios in the field of view. 30 



UPPER 

MONOCULAR 

(0.5-2.7 




FIG. 2-21. Zonal limits of comfortable flux 
distribution ratios. 



To determine if a lighting design or installation conforms to the criteria 
of comfort established by nature, the ratio of flux per unit solid angle in 
each zone of the field of view to the average flux per unit solid angle through- 
out the field is plotted in Fig. 2-21. 

To obtain the ratios, a true perspective or a photograph is prepared on 
which the zones of the field of view may be laid out in scale. Then the 
flux per unit solid angle in each zone and in the field may be obtained by 
dividing the integral of flux from all sources in a given zone by the solid 
angle subtended by that zone. 

5. Spatial brightness equilibrium. On assumptions similar to those just 
stated, another investigator has selected for analysis those natural scenes 
which immediately prior to sunset provide illumination of the order of 50 
to 100 footcandles. This illumination may be provided indoors by means 
of available light sources, and electric power supply and distribution sys- 
tems. It is suggested that comfort in this range will be assured if "spatial 
brightness equilibrium" comparable with that of the presunset period out 
of doors is maintained. 31 



LIGHT AND VISION 



2-27 



Direct Glare and Reflected Glare 

It is sometimes convenient to indicate by the terms direct glare or re- 
flected glare whether the glare effect is caused by the brightness of a glare 
source itself, or by its reflected image. (See Fig. 2-22.) 

Case 1: Both Object and Re- 
maining Area of 2 Degree Task 
Have Perfectly Diffuse Surfaces. 
Contrast between the detail 
and its background is inde- 
pendent of the orientation of 
the observer and the sources 
contributing to the brightness 
of the task. (Fig. 2-23 A.) 
Disability and discomfort glare 
criteria may be applied equally 
well to all brightnesses in the 
field of view, whether they are 
viewed directly or by reflec- 
tion. 

■Case 2: Object and Task 
Have Other Than Perfectly 
Diffuse Surfaces. Contrast 
between the detail and its back- 
ground is a function of the ob- 

FIG. 2-22. Method for determining zone in 
which potential glare sources may be located. 




G| * 




2" TASK 

(PERFECTLY 

DIFFUSE 

REFLECTANCE) 



(A) 




2" TASK 

(SPECULAR 

REFLECTANCE) 



FIG. 2-23A. When the task has a perfectly diffuse surface,, the disability and dis- 
comfort criteria applied to sources such as G in the field of view may be applied 
equally well to any source such as G\, G2, Gz, outside the field of view which 
contributes to the brightness of the task by reflection. B. When the task surface is 
specular the criteria may also be applied to sources outside the field of view, but 
only when the angle formed by eye and source with apex on the task is bisected by a 
normal to the task, as in the case of G\. 



2-28 



I E S LIGHTING HANDBOOK 



server's position and of the orientation of sources contributing to the bright- 
ness of the task as viewed by the observer (Fig. 2-23B). 32 Contrast must 
be computed separately for each orientation of contributing sources and 
observer and disability arid discomfort criteria may be applied only to those 
sources which do not contribute to the apparent task brightness viewed by the 
observer. 

Visibility of Luminous Signals 

Seeing luminous signals of the type projected by coastal lighthouses, 
airway beacons, and auto traffic lights involves the same factors of vision — 
size, background brightness, time, and Color contrast — which are known to 
be important* in other seeing problems. 

For experimental convenience in the laboratory, many tests are run to 
determine the visual threshold for a given task. Large safety factors are 
usually required when laboratory threshold data are applied to practical 
seeing tasks. 33 




1" 10" 1' 10' 1° 10° 50° 

ANGLE SUBTENDED AT EYE BY SOURCE 

FIG. 2-24. Threshold illumination 
required at the eye for seeing circular 
objects of different sizes (dark back- 
ground). 33 



10" 5 10" 3 10 _1 1 10 10 3 

BACKGROUND BRIGHTNESS IN FOOTLAMBERTS 

FIG. 2-25. Threshold illumination re- 
quired at the eye for seeing point sources 
viewed against backgrounds of different 
brightnesses. 33 



Size. For threshold visibility, a large source must produce greater illu- 
mination at the eye than a small one. This relationship for circular areas 
is shown in Fig. 2-24. Luminous signals may usually be considered to be 
"point" sources. 

Background brightness. The visibility of a point source is a function of 
the brightness of the background and surround, as shown in Fig. 2-25. 
Both contrast and the observer's adaptation level affect the threshold 
brightness. 34 

Time. For threshold visibility, the illumination at the eye produced by 
a flashing source must be greater than that produced by a steady source. 
The relationship is given by the equation: 



LIGHT AND VISION 2-29 

E_ _ t + a 

E = t 

where E = threshold illumination at the eye for 

a steady source (foot candles) 
E = threshold illumination at the eye for 

a flashing source (footcandles) 
t = duration of the flash (seconds) 
a = 0.21 second 

Note: It is assumed that the observer knows the location of the source 
and is looking toward it. 

If it is necessary to locate a flashing light of a known brightness (above 
threshold) when its approximate position is not known, the time con- 
sumed in searching for it is a function of its brightness and flash duration 
and of the area searched. 33 This is expressed: 

t = T MS -Vi) 
where t — average search time before finding source 

(seconds) 
T = duration of cycle (flash duration + dark 

period in seconds) 
</> = solid angle subtended by the area searched 

(steradians) 
S = external solid angle corresponding to 

retinal area for which the illumination 

produced by the source is above threshold 

(steradians) 

Color contrast. When it is necessary to recognize correctly which color 
of a multicolor signal system is viewed, the illumination produced at the 
eye must be greater than that required for merely detecting the presence 
of the same source. Usually the more complicated the system the higher 
the threshold for each color: to provide positive recognition of each color 
of a three-color system requires more illumination at the eye than that 
required for positive recognition of each color in a two-color system but 
not as much illumination as required from each color of a four- or five- 
color system. 

The individual spectral distribution characteristics of each color used in 
a system and their relationships also influence the value of illumination 
required at the recognition threshold. A system of colors of nonover- 
lapped spectral distributions with steep slopes requires less illumination 
at the recognition threshold- than a similar system with overlapping spec- 
tral distributions of gradual slope. 

Because small changes in atmospheric conditions as well as in spectral 
distributions cause appreciable differences in the illumination required at 
the threshold of recognition, great care must be taken in applying any ex- 
perimental data to new problems. 35 



2-30 



I E S LIGHTING HANDBOOK 
REFERENCES 



1. "Third Report of the Miners' Nystagmus Committee," Med. Research Council, H. M. Stationery 
Office, London, 1932. 

2. Kuhn, H. S., Indus/rial Ophthalmology, C. V. Mosby Company, St. Louis, 1944. Resnick, L., Eye 
Hazards in Industry, Columbia University Press, New York, 1941. 

3. Harmon, D. B., "Lighting and Child Development," Ilium. Eng., April, 1945. 

4. Osterberg, C, Topography of the Layer of Rods and Cones in the Human Retina, Copenhagen, 1935. 

5. Hecht, S. J., "Kinetics of Dark Adaptation," J . Gen. Physiol., November, 1921, and May, 1927. Hecht, 
S. J., "A Theory of Visual Intensity Discrimination," J. Gen. Physiol., May, 1935. "The Nature of the Photo- 
receptor Process," Handbook of General Experimental Psychology, Clark University Press, Worcester, Massa- 
chusetts, 1934. Lasareff, P.. PJluger's Arch.ges. Physiol., March, 1926. Putter, A., Pfluger's Arch ges Physiol 
191S. 

6. Wald, G., "Vision: Photochemistry," in Glasser's Medical Physics, Year Book Publishers, Inc. Chicago 
1944. 

7. Moon, P., and Spencer, D. E., "A Modified Photochemical Theory of Vision," J. Optical Soc. Am., 
January, 1945. 

8. Hartline, H. K., and Graham, C. H., "Nerve Impulses from Single Receptors in the Eye," J. Cellular 
Comp. Physiol., April, 1932. 

9. Hecht, S. J., "The Development of Thomas Young's Theory of Color Vision," J. Optical Soc. Am., 
Mav 1939 

10. LeGros Clark, W.E., J. Anat., Vol. 75, 1941. 

11. Lythgoe, R. J., "Measurement of Visual Acuity," Special Report No. 173, Med. Research Council, 
H. M. Stationery Office, London, 1932. Hartridge, H., "Visual Acuity and Resolving Power of the Eye," J . 
Physiol., London, December, 1922. 

12. Moon, P., and Spencer, D.E., "Visual Data Applied to Lighting Design," J . Optical Soc. Am., October, 
1944. 

13. Cobb, P. W., and Moss, F. K., "The Four Variables of the Visual Thres'iold," J. Franklin Inst., June, 
1928. 

14. Connor, J. P., and Ganoung, R. E., "An Experimental Determination of the Visual Thresholds at 
Low Values of Illumination," J. Optical Sec. Am., September, 1935. 

15. Cobb, P. W., "Some Experiments in the Speed of Vision," Trans. Ilium, ''ng. Soc, February, 1924. 

16. Ferree, C. E., and Rand, G., "Intensity of Light and Speed of Vision Stu ... id with Special Reference to 
Industrial Situations, Part I," Trans. Ilium. Eng. Soc, January, 1927. Also "intensity . . . Situations, Part 
II," Trans. Ilium. Eng. Soc, May, 1928. "Size of Object Visibility and Visnn," Trans. Ilium. Eng. Soc, 
October, 1931. 

17. Luckiesh, M., and Moss, F. K., The Science of Seeing, D. Van Nostrai Company, Inc., New York, 
1937. 

18. "I. E. S. Code of Practice for Good Lighting of Building Interiors inch ing Recommended Values of 
Illumination," Illuminating Engineering Society, (British), London, 1945. V ton, H. C, "Proposals for a 
New Lighting Code," Trans. Ilium. Eng. Soc, (British) London, February, . 

19. Recommended Practice of Industrial Lighting, Ilium. Eng. Soc, May, 194i, -iso American Standard A 11 
19^2, American Standards Association, New York. Recommended Practice of Office Lighting, Ilium. Eng. 
Soc, 1946. American Standard Practice of School Lighting, Ilium. Eng. Soc, 1946. Recommended Practice 
of Street and Highway Lighting, Ilium. Eng. Soc, 1946. Recommended Practice of Store Lighting, Ilium. Eng. 
Soc, 1946. 

20. Luckiesh, M., and Moss, F. K., "Visibility: Its Measurement and Significance in Seeing," J. Franklin 
Inst., October, 1935. 

21. Luckiesh, M., Light, Vision, and Seeing, D. Van Nostrand Company, Inc., New York, 1944. 

22. Luckiesh, M., and Moss, F. K., The Science of Seeing, D. Van Nostrand "'ompany, Inc., New York, 
1937. 

23. Moon, P., and Spencer, D. E., "On the Stiles-Crawford Effect," J. Optic 1 Soc. Am., June, 1944. 

24. Holladay, L. L., "The Fundamentals of Glare and Visibility," J. Optic Soc. Am., and the Review of 
Scientific Instruments, April, 1926. Stiles, W. W., "Recent Measurements of the ffect of Glare on the Bright- 
ness Difference Threshold," Proceedings of the International Commission on Illun ation, 1928. See also Dept. 
Sci. Ind. Research Paper No. 10, Appendix III, London, 1935. 

25. Moon, P., and Spencer, D. E., "The Specification of Foveal Adaptation," J. Optical Soc. Am., August, 
1943. Moon, P., and Spencer, D. E., "A Simple Criterion for Quality in Lighting," Ilium. Eng., March, 1947. 

26. Committee on Standards of Quality and Quantity for Interior Illumination, "Brightness and Bright- 
ness Ratios," Report No. 1, Ilium. Eng. Soc, December, 1944. •> 

27. Crouch, C. L., "Brightness Limitations for Luminaires," Ilium. Eng., July, 1945. Luckiesh, M., 
and Guth, S., "Discomfort Glare and Angular Distance of Glare-Source," Ilium. Eng., June, 1946. 

28. Harrison, W., "Glare Ratings," Ilium. Eng., September, 1945. Harrison, W., and Meaker, P., "Further 
Data on Glare Ratings," Ilium. Eng., February, 1947 

29. Moon, P., "Discussion of 'Glare Ratings' by Harrison," Ilium. Eng., September, 1945. Moon, P., and 
Spencer, D. E., "Visual Effect of Non-Uniform Surrounds," J. Optical Soc. Am , March, 1945. 

30. Logan, H. L., "Light for Living," Ilium. Eng., March, 1947. Slauer, R.G., " Discussion of 'Confusion 
in Brightness Thinking'," Ilium. Eng., February, 1945. Logan, H. L., "The Anatomy of Visual Efficiency," 
Ilium. Eng., December, 1941. Logan, H. L., "Specification Points of Brightness.'" Ilium. Eng., September, 
1939. 

31. Ainsworth, G., "Discussion of 'Lighting and Seeing in the Drafting Roorn' by W. G. Darley and G. S. 
Ickes," Ilium. Eng., December, 1941. 

32. Crouch, C. L., "The Relation between Illumination and Vision," Ilium. Ei Tovember, 1945. 

33. Lash, J. D., and Prideaux, G. F., "Visibility of Signal Lights," Ilium. Et^ "ovember, 1943. Stiles, 
W. S., Bennett, M. G., and Green, H. N., "Visibility of Light Signals with Sp Reference to Aviation 
Lights," H. M. Stationery Office, London, 1937. 

34. Knoll, H. A., Tousey, R., and Hulbert, E. O., "Visual Thresholds of Stea< Point Sources of Light in 
Fields of Brightness from Dark to Daylight," J . Optical Soc Am., August, 1946/ 

35. Blondell, A., and Rey, J., "The Perception of Lights of Short Duration at Their Range Limits," Trans. 
Ilium. Eng. Soc, November, 1912. Hulbert, E. O., "Optics of Atmospheric Haze," J . Optical Soc. Am., July, 
1941. McNicholas, H. J., "Selection of Colors for Signal Lights," ./. Research Nat. Bur. Standards, December, 
1936. Ornstein, Eymers, and Vermeulen, "Color Recognition Tests with Reference to the Suitability of 
Signal Glasses," K. Akad. Amsterdam, Proc 37.7, 1934. Woodside, C. S., "Identification Ranges for Colored 
Light Signals," Report No. 5, Electrical Section (660), Bureau of Ships, Navy Department, 1944. 



SECTION 3 

STANDARDS, NOMENCLATURE, ABBREVIATIONS, 

AND SYMBOLS 



Among the hundred or more national professional and trade organiza- 
tions engaged in standardization 1 in the United States, at least four 2 sponsor 
this work as their major activity. These co-operate with many other 
groups active in special fields, such as the Illuminating Engineering Society, 
and with state and 1 jderal governments. Their activities are reported in 
the monthly, Industrial Standardization, which is published by the Ameri- 
can Standards Association. New lighting practices appear in Illuminating 
Engineering, the monthly publication of the Illuminating Engineering 
Society. 

When a recommended practice or standard code 3 proposed by a profes- 
sional group involvwithe safety or welfare of the general public, it is some- 
times incorpor o+ -" >y the state legislatures in the state law. (See the 
index or Sev hrough 16 of the Application Division for condensed 

forms of the x es recommended by the Illuminating Engineering 

Society.) 

Because of Amei._an membership in various international groups, which 
comprise representatives of different nations, standardization in the United 
States is given international significance. The International Commission 
on Illumination, I.C.I. {Commission Internationale de VEclairage, CLE.), 
is the international organization concerned with illumination. 

1. Referent dards 

The ability easure physical quantities accuiately is essential to 

progress in all ph&^s of science and engineering. A fundamental step in 
developing this ability is the establishment of reference standards against 
which practical measuring tools may be calibrated. 

When such standards are physical objects, they are customarily pre- 
served at the National Bureau of Standards in Washington. An example 
is the set of carbon-filament lamps which has served as the American 
candlepower standard since 1909. Whenever possible, it is present prac- 
tice to replace such arbitrary physical objects, which might never be exactly 
duplicated if destroyed, with standards suited to convenient and accurate 
reproduction in ' oratories throughout the world. 

Standard. A •nary standard is one by which a unit of measurement is 
established and L n which the values of other standards are derived. A 
satisfactory primary standard must be reproducible from specifications. 

A secondary standard is calibrated by comparison with a primary 
standard. 

A working standard is any calibrated tool fcT daily use in measure- 
ment work. 

Note: References are listed at the end of each section. 

1 



3-2 I E S LIGHTING HANDBOOK 

Wavelength. The red cadmium spectrum line (0.64384696 micron in 
vacuum) has been established as the reference standard for all units of 
length. 

Velocity. The velocity (c) of all radiant energy, including light, is 
(2.99776 ± 0.00004) X 10 8 meters per second in vacuum 4 (approximately 
186,000 miles per second). In all material mediums the velocity is less 
and varies with the material's index of refraction and with wavelength. 

Candlepower. In the United States, the candle (unit of luminous in- 
tensity) equals (0.05857) times the average horizontal candlepower of 
the standard group of forty-five carbon-filament lamps preserved at the 
Bureau of Standards. Within the limits of uncertainty of measurement, 
this is identical with the international candle adopted in 1909. Each lamp 
is operated at a voltage which results in a practical color match within the 
group at approximately 2,097 Kelvin color temperature. 

In 1937, the International Committee on Weights and Measures adopted 
as the standard a blackbody operating at the temperature of freezing 
platinum. Its brightness was assigned the value of 60 candles per square 
centimeter. Candlepower values for standards having different spectral 
distributions may be obtained by the application of the luminosity factors 
(Table 1-3). This standard has not yet (1947) replaced the international 
candle adopted in 1909 by introduction into actual practice. The bright- 
ness of the new standard in terms of the 1909 unit is 58.9 candles per 
square centimeter. 

Luminosity. Since the 1924 agreement of the I.C.I. , Table 1-3 has been 
accepted internationally as representing the relative luminosity of the 
radiation of the wavelengths between 0.38 and 0.76 micron. 

2. American War Standards Relating to Color 

Various data related to color are included with some explanatory dis- 
cussion in Section 4. 

During World War II an American War Standard (ASA Z-44-1942) was 
developed to meet the recognized need for a method of describing and 
specifying color. 5 ' 6 ' 7 ' 5 - 9 ' 10 ' 11 - 12 ' 13 ' 14,15 ' 16 A Safety Color Code for marking haz- 
ards and identifying equipment (ASA Z-53.1-1945) was developed also. 17 

3. Standard Illuminants 

By international agreement in 1931 the I.C.I, adopted the trichromatic 
system for mathematical color specification and established as standards 
for colorimetry the illuminants A, B, and C. The relative energy distribu- 
tions of these illuminants are given in Table 3-1. 

The following specifications are for practical laboratory sources which 
have the distribution characteristics of the standard illuminants : 8 

Illuminant A is a tungsten lamp operated at 2,848 K color tempera- 
ture. However, for purposes of computation the data for a blackbody at 
2,848 K are used (c 2 = 14,350 micron-degrees). 



STANDARDS, NOMENCLATURE, ABBREVIATIONS 



3-3 



Illuminants B and C consist of illuminant A plus a filter. Illuminant B 
approximates a blackbody source operating at 4,800 K; it is used by the 
British as then daylight standard. Illuminant C approximates daylight 
provided by the combination of direct sun and clear sky light having a color 
temperature of approximately 6,500 K. The filters are made as follows: 

For illuminant B, the filter consists of a layer one centimeter thick of 
each of the following solutions, contained in a double cell constructed of 
white optical glass: 

No. 1 Copper sulphate (CuS0 4 -5H 2 0) 2.452 g 

Mannite (C 6 H 8 (OH) 6 ) 2.452 g 

Pyridine (C 5 H 6 N) 30.0 cu cm 

Distilled water to make 1000.0 cu cm 

No. 2 Cobalt-ammonium sulphate (CoS0 4 - (NH 4 ) 2 S0 4 -6H 2 0) . . 21.71 g 

Copper sulphate (CuS0 4 -5H 2 0) 16.11 g 

Sulphuric acid (density 1.835) 10.0 cu cm 

Distilled water to make 1000.0 cu cm 

For Illuminant C, an identical cell is used, but the solutions are : 

No. 1 Copper sulphate (CuS0 4 -5H 2 0) 3.412 g 

Mannite (C 6 H 8 (OH) 6 ) 3.412 g 

Pyridine (C 6 H 5 N) 30.0 cu cm 

Distilled water to make 1000.0 cu cm 

No. 2 Cobalt-ammonium sulphate (CoS0 4 - (NH 4 ) 2 S0 4 -6H 2 0) . . 30.5S0 g 

Copper sulphate (CuS0 4 -5H 2 0) 22.520 g 

Sulphuric acid (density 1.835) 10.0 cu cm 

Distilled water to make 1000.0 cu cm 



Table 3-1. Relative Energy Distribution of Illuminants A, B, and C 



WAVE- 


RELATIVE ENERGY 


WAVE- 


RELATIVE ENERGY 


LENGTH 








LENGTH 
(micron) 








(micron) 


A 


B 


C 


A 


B 


C 


0.380 


9.79 


22.40 


33.00 


0.580 


114.44 


101.00 


97.80 


.390 


12.09 


31.30 


47.40 


.590 


121.73 


99.20 


93.20 


.400 


14.71 


41.30 


63.30 


.600 


129.04 


98.00 


89.70 


.410 


17.68 


52.10 


80.60 


.610 


136.34 


98.50 


88.40 


.420 


21.00 


63.20 


98.10 


.620 


143.62 


99.70 


88.10 


.430 


24.67 


73.10 


112.40 


.630 


150.83 


101.00 


88.00 


.440 


28.70 


80.80 


121.50 


.640 


157.98 


102.20 


87.80 


.450 


33.09 


85.40 


124.00 


.650 


165.03 


103.90 


88.20 


.460 


37.82 


88.30 


123.10 


.660 


171.96 


105.00 


87.90 


.470 


42.87 


92.00 


123.80 


.670 


178.77 


104.90 


86.30 


.480 


48.25 


95.20 


123.90 


.6S0 


185.43 


103.90 


84.00 


.490 


53.91 


96.50 


120.70 


.690 


191.93 


101.60 


80.20 


.500 


59.86 


94.20 


112.10 


.700 


198.26 


99.10 


76.30 


.510 


66.06 


90.70 


102.30 


.710 


204.41 


96.20 


72.40 


.520 


72.50 


89.50 


96.90 


.720 


210.36 


92.90 


68.30 


.530 


79.13 


92.20 


98.00 


.730 


216.12 


89.40 


64.40 


.540 


85.95 


96.90 


102.10 


.740 


221.66 


86.90 


61.50 


.550 


92.91 


101.00 


105.20 


.750 


227.00 


85.20 


59.20 


.560 


100.00 


102.80 


105.30 


.760 


232.11 


84.70 


58.10 


.570 


107.18 


102.60 


102.30 











3-4 



1 E S LIGHTING HANDBOOK 



Nomenclature 

The precision required in the solution of engineering problems makes it 
necessary that both the oral and written language used by engineers in 
transmitting their ideas be precise. The standardization of terms and 
then proper use is therefore encouraged. 

The Illuminating Engineering Society has had a technical committee 
engaged in the development of the standard nomenclature of its field for 
more than thirty years. The report of this committee, Illuminating Engi- 
neering Nomenclature and Photometric Standards, adopted by the society 
in 1941 and approved in 1942 by the American Standards Association as 
ASA Z7-1942, is the most recent of many revisions published since the 
first appeared in 1910. 

Because of inherent limitations of the standard nomenclature it has been 
proposed from time to time that a completely different nomenclature more 
conveniently related to other scientific terms and with greater generality 
and international utility be adopted. 18 However, a language develops 
largely as a result of usage, and because of then far-reaching influence, 
changes in standard nomenclature are made very cautiously. See Table 3-2. 



Table 3-2. Standard Units, Symbals, and Defining Equations for 
Fundamental Quantities 



QUANTITY 


UNITS 


ABBREVIA- 
TIONS 


SYM- 
BOLS 


DEFINING EQUATIONS 


RADIATION— RADIOMETRY 


Radiant energy 


erg 

joule 

calorie 


J 
cal 


U 




Radiant energy 
density 


erg per cubic centi- 
meter 


erg cni~ 3 


u 


u = dU/dV 


Spectral radiant 
energy 


erg | 

joule fper micron 

caloriej 


erg m _1 
cal n ' 


U X 


U\ = dU/d\ 


Radiant flux 


erg- per second 
'watt 


erg sec~' 
w 


*P 


* = dU/dt 


Radiant flux 
density or ra- 
diancy 

'Radiant emit- 
tance 


watt per square 
centimeter 

*Watt per si/uare meter 


w cm -2 
w m -2 


w 


W = d$/dA 


Irradiancy 
* ' Irradiance 


watt per square cen- 
timeter 
*watt per square meter 


w cm~ 2 
w m -2 


H 


H = d$>/dA 


Radiant in- 
tensity 


watt per steradian 


W 0.-1 


J 


J = d$/dw 


Spectral radi- 
ant intensity 


watt per steradian 
per micron 


W w-i m _1 


Jx 


Jx = dJ/d\ 


Steradiancy 
*Radiance 


watt per steradian per 
square centimeter 

"watt per steradian per 
square meter 


W to -1 cm -2 
W or 1 m-2 


N 


N = dJ/(dA cos 8) 

6 = angle between line of sight and 
normal to surface considered 



STANDARDS, NOMENCLATURE, ABBREVIATIONS 



3-5 



Table 3-2 continued: 



QUANTITY 



UNITS 



ABBREVIA- 
TIONS 



SYM- 
BOLS 



DEFINING EQUATIONS 



LIGHTING— PHOTOMETRY 



Luminosity 


lumen per watt 


lm watt -1 


K 


K 


= n/*x 


factor 












Luminous flux 


lumen 

*lumerg/sec 


lm 


F 






^pharos 


\lumin 


flm 


W 






Quantity of light 


lumen-hour 


lm-hr 


Q 


Q. 


= J'Fdt {t in hrs) 


'luminous 


*talbot 


*lm-sec 






energy 












jphos 


\lumen-second 


tlm-sec 


to 


\Q 


= y Fdt (t in sec) 


\phosage 


\lumen-second per 
square meter 


flm-sec m -2 


w 


\w 


= 1/ A J" Fit (t in sec) 


Illumination 


footcandles 


ft-c 


E 


E 


= dF/dA 




lux 


be 






(A = area of surface illumi- 




phot 


ph 






nated) 


* Illuminance 






E 






\pharosage 


\lumtns per square 
■meter 


flm m~ 2 


W 


\D 


= dF/dA 


Luminous in- 


candle 


c 


I 


I 


= dF/dos 


tensity or can- 










(oi = solid angle through which 


dlepower 










flux from point source 
is radiated) 


Brightness 


candles per unit area 


c/in 2 


B 


B 


= dI(dA cos 6) 




stilb 


sb 






(6 = angle between line of sight 




apostilb 


lm m~ 2 






and normal to surface con- 
sidered) 




lambert 


L 










footlambert 


ft-L 


B' 


B' 


= xdI(dA cos 6) 




apparent 












footcandle 










'Luminance 












]Helios 


\blondel 


tbl 


\B 


\H 


= ir(dD/du) cos 4> 
(w = solid angle 
^ = angle of incidence of cen- 
tral ray) 


\Heliostnt 


jblondel per meter 


tbl m-» 


]G 


\o 


= dH/dr 












(r = distance along central ray) 



* p roposed by the Colorimetry Committee of the O.S.A. (nonstandard). 18 
t Proposed by Moon (nonstandard). 18 

Except where indicated the following material has been revised and con- 
densed for handbook publication from the standard nomenclature. The 
three subdivisions immediately following, on radiation, light, and light 
measurement, deal with fundamental concepts. 

1. Radiation Terms 

Radiant energy travels in the form of electromagnetic waves. 

Radiant energy density is radiant energy per unit volume. 

Spectral radiant energy is radiant energy per unit wavelength interval AX, 
at wavelength X. 

Radiant flux is the time rate of flow of radiant energy. 

Radiant flux density is the ratio of radiant flux at an element of surface 
to the area of the element. 



3-6 I E S LIGHTING HANDBOOK 

Steradiancy in a given direction is the radiant flux per unit solid angle, 
per unit of projected area of the source viewed from that direction. 

Irradiancy is the incident radiant flux per unit area. 

Radiant intensity is the radiant energy emitted per unit time, per unit 
solid angle about the direction considered. 

Spectral radiant intensity is radiant intensity per unit wavelength interval. 

2. Terms Relating to Light \ 

Light, for the purposes of illuminating engineering, is radiant energy 
evaluated according to its capacity to produce visual sensation. The 
evaluation is accomplished by multiplying the energy radiated at each 
wavelength by the standard luminosity factor for that wavelength and 

/•0.76 

adding the results: F = KxJ\d\. See Table 1-3. 

Jo.38 

x Luminous flux is the time rate of flow of light. 

Illumination is the density of luminous flux incident upon a surface. 
It equals the quotient of flux by the area of the surface when the flux is 
uniform over the area. 

- Luminous intensity is the solid angular luminous flux density in the 
direction in question. It equals the quotient of the flux on an element of 
surface by the angle subtended by the element when it is viewed from 
the source. 

Brightness is the luminous intensity of any surface in a given direction, 
per unit of projected area of the surface viewed from that direction. 

3. Basic Units of Light Measurement ) 

- The lumen is the unit of luminous flux. It equals the flux emitted 
through a unit solid angle (one steradian) from a point source of one candle. 

- The lumen-hour is the unit of light. It is the quantity of light delivered 
in one hour by a flux of one lumen. 

— The footcandle is the unit of illumination when the foot is the unit of 
length. It is the illumination on a surface, one square foot in area, on 
which is uniformly distributed a flux of one lumen. It equals lumens per 
square foot. See Fig. 3-1. 

The lux is the unit of illumination in the metric system. It equals 
lumens per square meter. 

The phot is the unit of illumination when the centimeter is the unit of 
length. It equals lumens per square centimeter. 

The candle is the unit of luminous intensity. 

Candlepower is luminous intensity expressed in candles. 

The apparent candlepower of an extended source (at a specified distance) 
is the candlepower of a point source which would produce the same illu- 
mination at that distance. 
T* The mean spherical candlepower of a lamp is the average candlepower 
of the lamp in all directions in space. It is equal to the total luminous 
flux (lumens) of the lamp divided by 47r. 



STANDARDS, NOMENCLATURE, ABBREVIATIONS 



3-7 



The mean horizontal candlepower of a lamp is the average candlepower in 
the horizontal plane passing through the geometrical center of the luminous 
volume of the source. It is assumed that the axis of symmetry of the source 
is vertical. 

""""-The footlambert is the unit of brightness equal to the average brightness 
of any surface emitting or reflecting one lumen per square foot. It equals 
l/V candle per square foot. This is also called the apparent footcandle. 

The lambert is the unit of brightness equal to the average brightness of 
any surface emitting or reflecting one lumen per square centimeter. It 
equals l/V candle per square centimeter. 






/ iV 



>t^1 Hjr foot 



N % 



va 

X 



FIG. 3-1. Relationship between 
candles, lumens, and footcandles. 

A uniform point source (luminous 
intensity or candlepower = 1 candle) 
is shown at the center of a sphere of 
1 foot radius. It is assumed that the 
sphere is perfectly transparent (i.e., 
has reflectance). 

The illumination at any point on 
the sphere is 1 footcandle (1 lumen per 
square foot). 

The solid angle subtended by the 
area, A, B, C, D is 1 steradian. The 
flux density is therefore 1 lumen per 
steradian, which corresponds to a 
luminous intensity of 1 candle, as 
originally assumed. 

The sphere has a total area of 12.57 
(4 it) square feet, and there is a lumi- 
nous flux of 1 lumen falling on each 
square foot. Thus the source pro- 
vides a total of 12.57 lumens. 



4. General Terms in Illumination 

angstrom: a unit of length equal to 10 -8 (one one-hundred -millionth) 
centimeter. 

micron: a unit of length equal to 10 -4 (one ten-thousandth) centimeter. 

x-unit: a unit of length equal to 10 -11 (one one-hundred-thousandth- 
millionth) centimeter. 

mega: a prefix meaning one million (10 6 ). 

kilo: a prefix meaning one thousand (10 3 ). 

milii: a prefix meaning one one-thousandth of (10 -3 ). 

micro: a prefix meaning one one-millionth of (10 -6 ). 

temperature radiator:* a radiator the radiant flux density (radiancy) of 
which is determined by its temperature and the material and character of 
its surface, and is independent of its previous history. 

blackbody:* a temperature radiator of which the radiant flux in all 
parts of the spectrum is the maximum obtainable from any temperature 
radiator operating at the same temperature ; will absorb all radiant energy 
falling upon it; practically realized in the form of a cavity with opaque 

* See Pages 1-8 and 1-12. 



3-8 I E S LIGHTING HANDBOOK 

walls at uniform temperature and with a small opening for observation 
purposes. 

gray body:* a temperature radiator the spectral emissivity of which is 
less than unity and the same at all wavelengths. 

total emissivity* (e,) : the ratio of the radiant flux density (radiancy) 
at an element of any temperature radiator to that at an element of a 
blackbody at the same temperature. 

spectral emissivity* (<? x ) : the ratio at a given wavelength of the radiant 
flux density per unit wavelength interval (at that wavelength) of any tem- 
perature radiator to that of a blackbody at the same temperature. 

5. Lighting Terms 

luminosity factor : the ratio of the luminous flux at a particular wave- 
length to the radiant flux at that wavelength. It is expressed in lumens 
per watt. The relative luminosity factor is a dimensionless ratio set equal 
to unity at 0.554 micron wavelength. Standard (relative) luminosity 
factors are given in Table 1-3. 

luminous efficiency of radiant energy : the ratio of the total luminous 
flux to the total radiant flux (usually expressed in lumens per watt of 
radiant flux). For energy radiated at a single wave-length, luminous 
efficiency is synonymous with luminosity factor. 

This term is not to be confused with the term efficiency as applied to a 
light source since the latter is based on the power consumed by the source 
instead of on the radiant flux from the source. 

mechanical equivalent of light (minimum) : the reciprocal of the luminous 
efficiency (maximum) of radiant energy; that is, the watts per lumen at 
the wavelength of maximum luminosity. 

The best experimental value is 0.00154 watt per lumen, corresponding to 
650 lumens per radiant watt, the maximum possible efficiency of a light 
source. When expressed in terms of the new value of the lumen these 
values become, respectively, 0.00151 watt per (new) lumen and 660 (new) 
lumens per watt. See page 1-12. 

efficiency (of a light source) : the ratio of the total luminous flux to the 
total power input, expressed in lumens per watt, or, (for combustion 
sources) in lumens per thermal unit consumed per unit of time. 

reflection factor (reflectance) (p or r) : the ratio of the light reflected by 
the body to the incident light. 

transmission factor (transmittance) (r or t) : the ratio of the light trans- 
mitted by the body to the incident light. 

performance curve: a curve representing the variation in performance 
of a lamp (candlepower, consumption, and so forth) during its life. See 
Fig. 6-39, page 6-43. 

characteristic curve : a curve expressing a relationship between two 
variable characteristics of a source, such as candlepower and volts, candle- 
power and rate of fuel consumption, and so forth. See Fig. 6-10, page 6-11. 

curve of light distribution : a curve showing the variation of luminous 

* See pages 1-8 and 1-12. 



STANDARDS, NOMENCLATURE, ABBREVIATIONS 3-9 

intensity of a lamp or luminaire with angle of emission. See Fig. 5-9b, 
page 5-17. 

solid of light distribution : a solid the surface of which is such that the 
radius vector from the origin to the surface in any direction is proportional 
to the luminous intensity of the light source in the corresponding direction. 

isocandle line : a line plotted on any appropriate co-ordinates to show 
directions in space, about a source of light, in which the candlepower is 
the same. See Fig. 8-17, page 8-47. 

isolux line: a line, plotted on any appropriate co-ordinates, showing 
points of equal illumination. See Fig. 8-20, page 8-49. 

coefficient of utilization (of an illumination installation) : the total flux 
received by the reference plane divided by the total flux from the lamps 
illuminating it. See Fig. 8-19, page 8-48. When not otherwise specified, 
the plane of reference is assumed to be a horizontal plane 30 inches (76 centi- 
meters) above the floor. See Table 8-2. 

lamp: a light source. 

electric filament lamp : a light source consisting of a glass bulb containing 
filament electrically maintained at incandescence ; commonly called an 
incandescent lamp, an electric light or a light bulb. 

electric discharge lamp : a lamp in which light is produced by the passage 
of electricity through a metallic vapor or a gas such as mercury, sodium, 
neon, argon, and so forth, enclosed in a tube or bulb ; sometimes called a 
vapor lamp. 

luminaire: a complete lighting unit including lamp, globe, reflector, 
refractor, housing, and such support as is integral with the housing. The 
term luminaire is used to designate completely equipped lighting fixtures, 
wall brackets, portable lamps, and so forth which are removable. It does 
not include permanent parts of a building, such as_a-ceiling, or other struc- 
tural element ; in street-lighting units the pole, or bracket is not considered 
a part of the luminaire. "~ 

color: the characteristics of light other than spatial and temporal 
inhomogeneities . 

Color of an object: the capacity of the object to modify the color of the 
light incident upon it. 

Colorants: substances used to produce the color of an object. 

Dominant wavelength (of a color): the wavelength that, combined with 
white light (equal energy spectrum) in suitable proportions, matches the 
color. 

Complementary wavelength: the wavelength that, combined with a sample 
color in suitable proportions, matches white light is the sample's comple- 
mentary wavelength. 

Purity: The relative brightnesses* of the spectrum and white compo- 
nents in the mixtures obtained in making a color match determine and are 
specified by purity. 

Colorimetric purity: the ratio of the brightness of the spectral component 
to the brightness of mixture obtained in making a color match. 

* Candancy and luminance have been proposed as being more appropriate terms. 



3-10 I E S LIGHTING HANDBOOK 

Excitation purity: the ratio of the distance from the white point to the 
point representing the sample to the distance along the same straight line 
from the white point to the spectrum locus or the purple boundary, both 
distances being measured on the I.C.I, chromaticity diagram. 

Chromaticity: the characteristics of light specified by dominant wave- 
length and purity. (Complementary wavelength and purity for purples.) 

Chromaticity diagram: a diagram on which chromaticities are represented 
by points independent of the choice of a standard quality white. See 
Fig. 4-6, page 4-12. 

Spectrum locus: the locus of points representing the colors of the visible 
spectrum in a chromaticity diagram. 

Purple boundary: the straight line drawn between the ends of the spec- 
trum locus. 

Blackbody locus: the locus of chromaticities of blackbodies having various 
temperatures. 

Locus of whites: points in a region of a chromaticity diagram representing 
qualities that may be considered white under circumstances of common 
occurrence. 

Three-color mixture: a mixture of suitable amounts of light of three 
suitably selected chromaticities with which a color may usually be matched. 

Color-mixture data: the amounts of the primaries required to establish 
a match. 

Transformation of color-mixture data: computations of color-mixture data 
for one set of primaries having data for another set. 

Luminosity coefficients: constants the sum of whose multiples by the 
three-color mixture data for any color give the brightness* of the color. 

Trichromatic coefficient: the ratio of any one of the color -mixture data 

for a sample to the sum of the three-color mixture data, x = v v „ 

A -f- i -j- Z 

Trichromatic co-ordinates: any pair of the trichromatic coefficients used 
as co-ordinates of a point in a plane representing the chromaticity of a 
sample (x, y). 

I.C.I, standard illuminants for colorimetry: the three illuminants adopted 
by the I.C.I, for use in colorimetry are designated A, B, and C. Selected 
ordinates for Illuminants A, B, and C are given in Table A-13, page A-28. 

Indirect colorimetry: color-mixture data for any sample computed from 
the data for the spectrum and the spectral distribution of the sample. 

Selected ordinate method of colorimetric calculation: a method of avoiding 
the numerous multiplications of indirect colorimetry by summing the 
spectral distribution data for specially selected, nonuniformly spaced 
wavelengths. See pages 4-16 and A-24. 

6. Ultraviolet Radiation Terms 

erythemal flux : radiant flux evaluated according to its capacity to pro- 
duce erythema (temporary reddening) of the untanned human skin. 

* Candancy and luminance have been proposed as being more appropriate terms. 



STANDARDS, NOMENCLATURE, ABBREVIATIONS 3-11 

relative erythemal factor: a factor which gives the relative erythemal 
effectiveness of radiation of a particular wavelength as compared with that 
of wavelength 0.2967 micron, which is rated as unity. 

unit of erythemal flux (E-viton, erytheme) : an amount of radiant flux 
which will give the same erythemal effect as 10 microwatts of radiant energy 
at 0.2976 micron. 

onsen : the recommended practical unit of erythemal flux density. It 
equals one unit of erythemal flux per square centimeter. 

erythemal exposure : the product of erythemal flux density on a surface 
by the duration of the exposure. It equals the amount of effective radiant 
energy received per unit of area exposed. 

7. Electrical Terms 

There are two types of electric currents: alternating (ac) and direct (dc). 
By alternating current is meant a current which changes its direction of 
flow at regular intervals, and by direct current, one that continues to flow 
in one direction. The frequency of alternating current is the total number 
of times the current flows in each direction per second. Most alternating 
current in the United States has a frequency of 60 cycles per second. 19 

In an a-c circuit the alternation of the current is not always in step (in 
phase) with the voltage. If the current lags behind the voltage, the circuit 
is said to contain inductance and if the current leads the voltage, the circuit 
is said to have capacitance. Reactance is the general term that correctly 
designates both inductance and capacitance. 

In an a-c circuit containing reactance, the power consumed is not given 
by the product of the voltage and current alone and thus cannot be deter- 
mined from the measurement of the current and voltage but must be 
measured by a wattmeter. The ratio of the wattage to the product of the 
current and voltage is called the power factor of the circuit. For a circuit 
containing resistance only, the power factor is unity. For any other circuit 
the power factor is a proper fraction. 

The phenomenon that occurs on making or breaking a circuit containing 
inductance or capacitance is called a transient. If a voltage is suddenly 
applied to a circuit containing capacitance, there is an initial rush of current 
exceeding the steady current which will be maintained by the same voltage, 
but when an inductive circuit is broken an electromotive force is developed 
which tends to cause the current to continue to flow. 

electromotive force: the potential difference (pressure) measured in 
volts required to cause a current of electricity, measured in amperes, to 
flow through a resistance, measured in ohms. 

fundamental units : the ampere, a unit defined as the current which will 
deposit 1.118 milligrams of silver per second in a voltameter under certain 
specified conditions ; and the ohm, a unit equal to the resistance at 0C of a 
column of mercury 106.3 centimeters long of constant cross section and 
having a mass of 14.4521 grams. 

watt : a unit of electric pow T er equal to the power required to maintain 
a current of one ampere through a resistance of one ohm. 



3-12 



I E S LIGHTING HANDBOOK 



Abbreviations for Scientific and Engineering Terms 2C 



A 

absolute abs 

alternating current (as noun) 

spell out or ac 
alternating-current (as adjective) 

spell out or a-c 

ampere amp 

ampere-hour amp-hr 

Angstrom unit A 

antilogarithm antilog 

atmosphere atm 

atomic weight at. wt 

avoirdupois advp 

azimuth az or a 

B 

boiling point bp 

British thermal unit Btu or B 

C 

calorie cal 

candle c 

candlepower cp 

centimeter cm 

centimeter-gram-second (system) . . . .cgs 

chemically pure cp 

circular mils cir mils 

coefficient coef 

cologarithm colog 

conductivity pond 

constant const 

cosecant esc 

cosine cos 

cotangent cot 

coulomb spell out 

counter electromotive force cemf 

cycles per second spell out or c 

D 

decibel db 

degree deg or ° 

degree centigrade C 

degree Fahrenheit F 

degree Kelvin K 

diameter diam 

direct current (as noun) . . . spell out or dc 
direct-current (as adjective) 

spell out or d-c 

E 

efficiency eff 

electric elec 

electromotive force emf 



F 

farad spell out or f 

feet per minute fpm 

feet per second f ps 

foot ft 

footcandle ft-c 

footlambert ft-L 

foot-pound -second (system) fps 

freezing point fp 

frequency spell out 

fusion point fnp 

G 

greatest common divisor gcd 

II 

henry h 

horsepower hp 

horse-power-hour hp-hr 

hour hr 

hundred C 

I 

inch in 

inches per second ips 

inside diameter ID 

J 

joule j 

K 

kilocalorie kcal 

kilocycles per second kc 

kilogram kg 

kilometer km 

kilometers per second kmps 

kilovolt kv 

kilovolt-ampere kva 

kilowatt kw 

kilowatthour kwhr 

L 

lambert L 

latitude ■ lat or $ 

least common multiple lem 

logarithm (common) log 

logarithm (natural) log or In 

longitude long, or X 

lumen lm 

M 

mass spell out 

maximum max 



STANDARDS, NOMENCLATURE, ABBREVIATIONS 3-13 



mean horizontal candlepower mhcp 

megacycle spell out 

megohm spell out 

melting point mp 

mho spell out 

microampere n a or mu a 

microfarad juf 

micromicrofarad ^i 

micron n or mu 

microvolt fiv 

microwatt ^w or mu w 

mile spell out 

miles per hour mph 

milliampere ma 

milligram rag 

millihenry mh 

millimeter mm 

millimicron im* or m mu 

minimum min 

minute min 

minute (angular measure) ' 

molecular weight moi. wt 

N 
National Electrical Code NEC 



ohm spell out or £2 

ohm-centimeter ohm-cm 

outside diameter OD 

P 

parts per million ppm 

per / (for tables, not recommended in 
text matter) 

potential spell out 

power factor spell out or pf 

R 

radian spell out 

reactive kilovolt-ampere kvar 



reactive volt-ampere var 

revolutions per minute rpm 

revolutions per second rps 

root mean square rms 



S 



secant sec 

second (angular measure) " 

sine sin 

specific gravity sp gr 

specific heat sp ht 

square sq 

square centimeter sq cm or cm 2 

square foot sq ft 

square inch sq in. 

square kilometer sq km or km 2 

square meter sq m or m 2 

square micron sq n or sq mu or ju 2 

square millimeter sq mm or mm 2 



tangent tan 

temperature temp 

thousand M 



volt 



volt-ampere va 

volt-coulomb spell out 



W 



watt w 

watthour whr 

weight wt 



Y 



yard 
year. 



•yd 
• yr 



Common Symbols 21 

In technical literature many symbols are used to save space and for 
convenience in setting up equations. The following are common : 

Mathematics 



+ plus 

— minus 

± plus or minus 

X multiplied by 

-5- divided by 

= equal to 

^ not equal to 



nearly equal to 
identical with 
not identical with 
equivalent 
difference between 
difference 
congruent with 



> greater than 

5 not greater than 

< less than 

5 not less than 

: is to; ratio 

: : as; proportion 

7-t- geometric proportion 



3-14 



I E S LIGHTING HANDBOOK 



= approaches 
— > approaches limit of 
a varies as 
|| parallel to 
j_ perpendicular to 
Z angle 
^ arc of circles 



i equilateral 

= equiangular 

\/ radical ; root ; square root 

\/ cube root 

■\/ fourth root 

2 sum 

I product; factorial 



°c infinity 
/ integral 
•f function 
9 or 5 differential; variation 
ir pi 

.'. therefore 
v because 



Physics and Chemistry 



EP horsepower 
A increment 
* magnetic flux 

^ dielectric flux; electrostatic flux 
p resistivity 
7 conductivity 
A equivalent conductivity 
i precipitate 



01 reluctance 
— * direction 
*=> electrical current 
pH potential hydrogen 

\ y benzene ring 

~-> yields 

*=* reversible reaction 
T gas 



REFERENCES 

1. Martino, R. A., Standardization Activities of National Technical and Trade Organizations, National 
Bureau of Standards, misc. publication M169. Knowlton, A. E., Standard Handbook for Electrical Engineers 
Seventh Edition, Section 25, McGraw-Hill Book Company, Inc., New York, 1941. 

2. American Standards Association, American Society for Testing Materials, Central Committee for 
Lumber Standards, National Aircraft Standards Committee. 

3. American Standards , Booklet 4501, American Standards Association, New York, 1945, lists current 
standards. 

4. Birge, R. T., "General Physical Constants, " .Report on Progress in Physics, Physical Society, London, 
August, 1941. 

•, "A New Table of Values of the General Physical Constants," Reviews of Modern Physics, October, 

1941. 

5. Method of Test for Spectral Apparent Reflectivity of Paints, D 307-39, American Society for Test- 
ing Materials. 

6. Proceedings, Eighth Session, Commission Internationale de VEclairage, Cambridge, England, September, 
1931. 

7. Judd, D. B., "The 1931 I.C.I. Standard Observer and Coordinate System for Colorimetry," J. Optical 
Soc. Am., October, 1933. 

8. Hardy, A. C, Handbook of Colorimetry , Technology Press, Cambridge, Massachusetts, 1936. 

9. Judd, D. B., "A General Formula for the Computation of Colorimetric Purity," J. Research Nat. Bur. 
Standards, May, 1931. 

10. MacAdam, D. L., "Photometric Relationships between Complementary Colors," J. Optical Soc. Am., 
April, 1938. 

11. Munsell Book of Color (standard edition with complete explanatory matter; abridged edition adapted 
for comparisons), Munsell Color Company, Baltimore, Maryland, 1929. 

12. Glenn, J. J., and Killian, J. T., "Trichromatic Analysis of the Munsell Book of Color," J. Optical Soc. 
Am., December, 1940. 

13. Judd, D. B., and Kelly, K. L., "Method of Designating Colors," J. Research Nat. Bur. Standards, 
September, 1939. 

14. Nickerson, D., Use of the I.C.I. Tristimulus Values in Disk Colorimetry, U. S. Dep. Agr., May, 193S; 
mimeograph copies obtainable on request. 

15. Newhall, S. M., "Preliminary Report of the O.S.A. Subcommittee on the Spacing of the Munsell 
Colors," J. Optical Soc. Am., December, 1940. 

16. Nickerson, D., "Central Notations for ISCC-NBS Color Names," J. Optical Soc. Am., September, 1941. 

17. Highway Transportation: American Standard Manual on Uniform Control Devices for Streets and 
Highways, D6-1935. American Standard Adjustable Face Traffic Control Signal Head Standards, DW.1-1943. 
American Standards Associations, New York. Railroad Transportation: Standard Cade of the Association of 
American Railroads; Operating Rules; Block Signal Rules, Interlocking Rules. Navigation of Waterways: U. S. 
Coast Guard Introduction and Explanation of Light Lists, Atlantic and Gulf Coasts, Pacific Coast, and Intra- 
coastal Waterways. Air Navigation: Civil Aeronautics Administration publications establishing color light 
markings: Obstruction Marking Manual; Standard Specifications for Airport Lighting; ANC Specifications; 
Civil Air Regulations; Airway Engineering Specifications on Code Beacons and Course Lights. 

18. Moon, P., "A System of Photometric Concepts," J. Optical Soc. Am., June, 1942. Committee on 
Colorimetry, Optical Soc. Am. "The Psychophysics of Color," J. Optical Soc. Am., May, 1944. 

19. American Standard Definitions of Electrical Terms, ASA C42, 1941. Am. Inst. Elec. Eng., New York. 
Knowlton, E., Standard Handbook for Electrical Engineers, Seventh Edition, McGraw-Hill Book Company, 
New York, 1941. Pender, H, Del Mar, W.A., Mcllwain, K., Electrical Engineers' Handbook, John Wiley & 
Sons, Inc., New York. 

20. American Standard Abbreviations of Scientific and Engineering Terms, ASA Z10. 1-1941, American 
Standards Association, New York. 

21. Style Manual, Current EditionU. S. Government Printing Office. 



SECTION 4 
COLOR 



Colored light and colored surfaces may be produced, applied, per- 
ceived, and appreciated because of both their utility and decorative effect. 
Whether the primary objective is beauty or utility, the final result will 
almost always be a combination of some degree of both. Therefore it is 
desirable to give careful consideration to both the aesthetic and the func- 
tional phases of all problems involving color. 

Various ramifications of color involve chemistry, physics, physiology, 
psychology, and fine arts, as well as good taste. Ordinarily the skills 
utilized in the development of decorative color schemes for products, 
packages, interiors, or exteriors are quite different from those required for 
the measurement and specification of color. Whereas the artist may be 
expected to create an aesthetically harmonious scheme, it remains for the 
physicist and the engineer by numerical specifications of colors to provide a 
certain and unambiguous means of translating the conceptions of the de- 
signer into production. It is also a technical problem to maintain produc- 
tion of the same color unchanged over a considerable period and in widely 
separated plants, and later to reproduce a color which has been out of 
production for a considerable time. 

The illuminating engineer is concerned with color problems because light 
is an important factor related to the ultimate aesthetic and functional 
success of any color scheme. Also, the utility, appearance, and aesthetic 
effect of a lighting design may be influenced appreciably by the colors of 
surfaces in the illuminated area. 

Because of the wide differences which exist between the immediate inter- 
ests, experience, and training of indivi duals engaged in the several phases 
of color work, the possibility for misunderstanding between them is great. 
During W T orld War II, the American Standards Association adopted an 
Emergency Standard, Z44-1942, in order to eliminate such misunder- 
standing and many wastefully divergent practices. This standard recom- 
mends a method of physical measurement (spectrophotometry) as the 
fundamental process in the standardization of color. > (See page 4-24.) The 
standard also recommends the use of basic color specifications which can 
be computed from fundamental spectrophotometric data by a method 
adopted by the International Commission on Illumination. For the popu- 
lar interpretation of these basic color specifications, which might otherwise 
be incomprehensible to most people, the Standard recommends the use of 
descriptive I.S.C.C.-N.B.S. color names, which can be determined from 
the basic color specifications, "wherever general comprehensibility is desired 
and precision is not important." 

The I.S.C.C.-N.B.S. system of color names described on page 4-6 sup- 
plements the fundamental technical color terminology included in Section 3. 

Note: References are listed at the end of each section. 

1 



4-2 I E S LIGHTING HANDBOOK 

It is not suggested that the I.S.C.C.-N.B.S. names will replace either the 
numerical specifications or the trade names which manufacturers of tex- 
tiles, wall coverings, tiles, paint, and so forth, have been using conveniently 
for many years, but rather that they may assist in correlating and expedit- 
ing all color work. 

Color and Visual Performance 

From a practical standpoint, when compared on an equal-lumen basis, 
colors of light emitted by common illuminants are about equally satis- 
factory for most seeing problems. Apparently the only major exception 
occurs when the seeing problem involves color discrimination. The color 
of light most effective for discriminating some surface colors is among the 
least effective for discriminating others. The increase and decrease of 
brightness contrasts between colored objects in consequence of differential 
increase and decrease of their luminous reflectance is the major effect of 
different illumination colors. 1 (See Color Grading, page 4-17.) 

The color of walls, furniture, and other equipment seems to influence 
comfort and efficienc3 r , but insufficient data are available to permit develop- 
ing harmonious color combinations on a strictly engineering basis. Since 
taste and emotional reactions are involved in any evaluation of the results, 
it is probable that the solution of aesthetic design problems will continue 
to be based in good part on experience and judgment for some time, despite 
the existence of several proposals whereby solutions ma}^ be obtained 
through the application of mathematical formulas. (See page 4-16.) 

Color combinations and contrasts for working areas. The effects on seeing 
of contrast between task and background and of brightness and brightness 
distribution in the field of view are discussed in Section 2. However the 
data apply to tasks which for the most part involve black objects on white 
backgrounds. If it is desirable to have contrast but at the same time nearly 
uniform brightness in the field of view, color may be used. 

Few studies have been made to determine the effect of the color and 
brightness of surrounding surfaces on the utilization of light for seeing. 2 
"^jSurfacc colors and luminous reflectance. The luminous reflectances of 
surfaces vary with their color and with the light source used for illumination. 
Luminous reflectances are of major importance in lighting design since 
they influence brightness and flux distribution ratios, and illumination 
levels. The quantitive effects of the luminous reflectance and color of 
wall materials have been studied both by direct measurement and by mathe- 
matical analysis. It may be stated positively that light walls and ceilings, 
whether white or colored, are much more efficient than dark walls in con- 
serving light and in distributing it uniformly. 3 

In Fig. 4-1, photographs of a room in an industrial building before and 
after interior modifications were made are shown with sketches which 
suggest the step by step changes in luminous reflectance and color scheme. 3 
The results of these changes in terms of footcandles and utilization coeffi- 
cients also are indicated. 



COLOR 



4-3 




COLOR R* 



T 



WHITE 
AND 
GRAY_ 



DARK 
-RED- 



J- 



WHITE — 85- 



WHITE 

AND 

RUSSET 



DARK 
-OAK- 



BLOND 

i 



AVERAGE 

FOOTCANDLES 

2g3 , UTILIZATION 

S23 COEFFICIENT 



V//////////7A 



F7J?3 



YWtifM^A 



\yyy / y////yym>,„ 



u-/WMtf//Y.W/m 



■': , „ i 



1 : ,•,,■,:. 't 



* REFLECTANCE 



(D) 



10 20 30 40 50 60 



FIG. 4-1. Effect of color scheme on appearance, coefficient of utilization, and illu- 
mination level in a small room in an industrial area. 3 (A) Test room before changes 
in color scheme. (5) Step by step changes. (C) Test room with light walls, ceiling, 
floor, and furniture. (D) Variation of illumination and utilization coefficient with 
color scheme. 



4-4 



t E S LIGHTING HANDBOOK 



The results of a mathematical analysis of the effect of wall colors on 
illumination and brightness ratios in cubical rooms, having white ceilings 
(r = 0.80), totally indirect lighting, and black floors (r = 0.00), are given 
in Fig. 4-2. An increase of wall reflectance by a factor of 9 may result in an 
increase of illumination by a factor of about 3. Although the walls in 
rooms having low ceilings as compared with their length and width exhibit 
less control than in cubical rooms, wall reflections exert an appreciable 
influence when the ratio of length to width to height is as great as 23 : 10 : l. 4 



) 0.4 0.6 0.8 1.0 1.2 1.4 |.( 

CEILING BRIGHTNESS 

CEILING BRIGHTNESS (NO INTERREFLECTIONS) 




^WALL 
REFLECTANCE 
= 0.78 
TAKEN AS 
REFERENCE 
POINT 



0.2 0.4 0.6 0.8 1.0 1.2 1.4 

AVERAGE ILLUMINATION (DESK LEVEL) 
\ OBTAINED WITH \ 

'reflectance r= 





BB | 

iam2 












4 10.5 












F 








7 
i 


20— - 
1 1 



12 3 4 5 

ADAPTATION BRIGHTNESS 



I 2 3 

ADAPTATION BRIGHTNESS 



0.1 0.2 0.3 0.4 0.5 
ADAPTATION BRIGHTNESS 



WALL BRIGHTNESS (DESK LEVEL) WALL BRIGHTNESS (NEAR CEILING) CEILING BRIGHTNESS 





KEY 




r = 


1 


0.893 


2 


0.780 


3 


0.575 


4 


0.302 


5 


0.164 


6 


0.447 


7 


0.106 



0.05 0.10 0.15 0.20 0.25 0.30 0.1 0.2 0.3 0.4 0.5 0.6 0.7 

WALL BRIGHTNESS (DESK LEVEL) WALL BRIGHTNESS (NEAR CEILING) 

CEILING BRIGHTNESS CEILING BRIGHTNESS 

FIG. 4-2. Effect of wall colors on illumination and brightness ratios in a cubical 
room. (Neutral white ceiling r = 0.80; neutral black floor r = 0.00; totally indirect 
lighting.) 4 (/) White wallboard r = 0.893, (2) White asphalt tiles r = 0.780, (3) 
Cream washable fabric r = 0.575, (4) Cream asbestos board r = 0.302, (5) Gray 
asbestos board r = 0.164, (6) Primavera wood r = 0.447, (7) Walnut wood r = 0.106. 



Hues versus neutral gray for wall surfaces. When a colored and a gray 
surface of equal luminous reflectance are equally illuminated with light 
direct from an illuminant they will be equally bright. However, if a con- 
siderable portion of the light reaching the working surface has undergone 
several reflections from troughs and walls, as is usually the case in indirect 
or semi-indirect lighting, greater illumination will be obtained if those 
surfaces are colored than if they are grays of the same luminous reflectance. 
The amount of this improvement is shown in Fig. 4-3 for yellow, blue- 
green, and pink walls in comparison with gray walls having the same 
luminous reflectances. The greater the number of inter-reflections, the 
greater is the advantage to be gained. In the case of the blue-green and 



COLOR 



4-5 



pink walls, when the light has suffered 
five successive reflections before reach- 
ing the work surface, as in an indirect 
system, the illumination may be twice 
as great as would be obtained with 
gray walls of equal luminous reflec- 
tance. The magnitude of this effect 
can be computed for any surface by 
multiplying the spectral reflectances at 
the selected ordinates by themselves 
as many times as the number of inter- 
reflections. In all cases, the average 
of these products will be greater if the 
reflectance varies throughout the spec- 
trum than if it is constant (as in the 
case of a gray surface) at a value equal 
to the luminous reflectance of the sur- 
face color for the first reflection. The 
color of the light after numerous inter- 
reflections differs from the color of light 
direct from the source and is always 
such that the luminous reflectance of 
the colored walls is higher for it than 
for the color initially emitted by the 
lamps. If the walls are blue, then the 
light which has been reflected several 
itially emitted by the illuminant. 




12 3 4 5 

NUMBER OF REFLECTIONS 

FIG. 4*3. Comparison of inter- 
reflection efficiencies of colored and 
neutral surfaces having the same 
luminous reflectance. 



times is more blue than that in- 



Color Names and Notations 

The lack of precision characteristic of many terms used in everyday 
speech contributes to the difficulty encountered in preparing specifications 
which must be unambiguous and enforceable and yet at the same time 
understandable to a layman. 

In some cases, the efficient statement of color specifications sufficiently 
precise to satisfy the layman requires the use of carefully defined but 
unfamiliar technical terms. Fortunately such precision is not always 
necessary and a simple system of color designation developed by the Inter- 
Society Color Council in co-operation with the National Bureau of Stand- 
ards often will be found adequate. 

The notation and charts of the Munsell and Ostwald systems are well 
known. In addition, there are many other collections of physical color 
samples in use which offer practical utility to persons who understand their 
principles and purpose. 6 

Webster's New International Dictionary: 150 samples in 1946 unabridged 
edition. 



4-6 I E S LIGHTING HANDBOOK 

Dictionary of Color: Over 7,000 samples, with color names based on his- 
torical origins and current usage. By A. Maerz and M. Rea Paul. 
McGraw-Hill Book Company, New York. 

Ridgway: About 1,000 samples, each identified by name, widely used 
by archaeologists and naturalists. Robert Ridgway, Washington, 1912. 

Textile Color Card Association of the United States, Inc.: Issues standard 
and seasonal cards in dyed silk, the accepted authority in the textile 
industry. 200 Madison Avenue, New York. 

Hiler Color Chart: 162 color samples showing mat and gloss finishes with 
card index box containing masks and matching apertures. Favor, Ruhl & 
Company, Chicago and New York. 

Color Kit: Color identification achieved through the use of disks and a 
mechanical spinning device. Designed by Birren, The Crimson Press, 
Westport, Connecticut. 

Nu-Hue Color Directory: Over 1,000 paint samples with convenient 
matching placques and precise mixing formulas for each. Any color can 
be purchased by the gallon at retail. Martin-Senour Company, Chicago. 

Plochere Color Guide: Over 1,000 color samples, with paint mixing for- 
mulas for each. G. Plochere, 1820 Hyperion Avenue, Los Angeles. 

American Colorist: Contains over 500 samples, widely used in horti- 
culture, art, and industry. Developed by Birren, The Crimson Press, 
Westport, Connecticut. 

I.S.C.C.-N.B.S. system of color designation. Known as the "Inter-Society 
Color Council — National Bureau of Standards System," this plan was ap- 
proved by the Color Council in 1939 for use in the drug and chemical fields. 7 
The designations are equally appropriate and useful for other applications, 
and it is likely that they will be adopted gradually for general use. The 
system provides 312 color names, each of which designates one block of 
the Munsell color solid. Munsell notations for the boundary colors of 
each block have been determined. 5 Spectrophotometric measurement of 
the spectral reflection characteristics of the standard Munsell color chips 
have been made and these data have been transposed into the I.C.I. 
co-ordinates for illuminant C (standard daylight). Therefore, it is con- 
venient to convert a color name, having meaning to the layman, into 
Munsell notation having significance for the decorator, and into I.C.I. 
co-ordinates, which are familiar to the colorimetrist. 

Standard names and hue abbreviations are given in Table 4-1. Central 
Munsell notations for each block are given in Appendix Table A-14, 
page A-29. 

Since there are likely to be many distinguishable (though very similar) 
colors in each of the 312 Munsell blocks, the use of the names is limited in 
accuracy. If a more accurate specification is necessary, numerical notation 
(Munsell or I.C.I.) may be used. 

The greatest accuracy and precision in color specification may be obtained 
through the intelligent use of spectrophotometric curves. This method 
is basic and is widely used in the United States, having been made a part 
of ASA Z44-1942. 



COLOR 



4-7 



Table 4-1. I.S.C.C.-N.B.S. Standard Hue Names and Abbreviations 7 



NOUN 
FORM 



ABBREVI- 
ATION 



pink 

red 

orange 

brown 

yellow 

olive 

green 

blue 

purple 

white 

gray 

black 



Pk 

R 



Br 

Y 

01 

G 

B 

P 

Wh 

Gr 

Bk 



ADJECTIVE 
FORM 



ABBREVI- 
ATION 



pinkish 

reddish 

orange 

brownish 

yellowish 

olive 

greenish 

bluish 

purplish 



pk 
r 
o 
br 

y 

ol 

g 

b 
P 



ADJECTIVE 
MODIFIER 


ABBREVI- 
ATION 


light 
dark 


It 

dk 


weak 


wk 


strong 
moderate 


str 
mod 


medium 


med 


vivid 


V1V 


ADVERB 
MODIFIER 


ABBREVI- 
ATION 


very 


V 



Capitalized abbreviations refer to the noun form, lower case signifies the adjective form. 

Systems of Transparent Color Standards 

Color specifications based upon transparent mediums take advantage of 
the fact that it is possible with a fixed illuminant to control the color of the 
transmitted light over a wide range by introducing varying amounts of 
three absorbing materials, permitting the light to pass through two or more 
elements of the absorbing medium instead of through a single element. 
The color specification consists of the number of unit elements of each of 
the three absorbing components required to produce the color match by 
subtractive combination. 

The Lovibond system utilizes combinations of standardized glass filters 
of different thickness. 8, 10 - "• 12 The Army system utilizes combinations 
of standardized filter solutions of variable concentration. 13 

Such color systems are best suited to the specification of the color of 
other transparent mediums because it is usually easy to assure that stand- 
ard and sample receive the same amount and kind of illumination. Under 
those circumstances departure from a standard illuminant usually produces 
only a second-order effect upon the color specification. 9 



Munsell and Ostwald Systems of Surface Color Designation 

The color designation systems utilizing physical samples developed 
respectively by Albert H. Munsell, a Boston art teacher, and by Wilhelm 
Ostwald, a German, winner (1909) of the Nobel Prize in chemistry, are 
the two most widely known and used in the United States for designating 
surface colors. Each system is based on an orderly classification of opaque 
surface-color samples which lends itself readily to arrangement in the color 
solids shown in Fig. 4-4. 

Munsell system. In the Munsell system, a color is designated according 
to its value, chroma, and hue. The color solid is divided along its vertical 
axis into equally perceptible value units; along radii into equally perceptible 
chroma units, and angularly into equally perceptible hue units. 



4-8 



I E S LIGHTING HANDBOOK 



Any value unit equals every other value unit and any chroma unit equals 
every other chroma unit, but in perceptibility, value units do not equal 
chroma or hue units except by chance. Hue units equal each other only 
for fixed levels of both value and chroma. 14 

The relationship between Munsell value units and reflectance is shown 
in Table 4-2. To convert from Munsell notation to I.C.I, co-ordinates, 
see page 4-14. 

Table 4-2. Relationship between Munsell Value and 
Luminous Reflectance 





LUMINOUS REFLECT- 




LUMINOUS REFLECT- 


MUNSELL VALUE 


ANCE 
(Relative to smoked layer 


MUNSELL VALUE 


ANCE 

(Relative to smoked layer 




of magnesium oxide*) 




of magnesium oxide*) 


10.0 


102.6 


7.8 


55.6 


9.9 


100 


7.7 


53.9 


9.8 


97.4 


7.6 


52.3 


9.7 


94.9 


7.5 


50.7 


9.6 


92.4 


7.4 


49.1 


9.5 


90 


7.3 


47.5 


9.4 


87.7 


7.2 


46 


9.3 


85.3 


7.1 


44.5 


9.2 


83.1 


7.0 


43.1 


9.1 


80.8 


6.5 


36.2 


9.0 


78.7 


6 


30 


8.9 


76.5 


5.5 


24.6 


8.8 


74.4 


5 


19.8 


8.7 


72.4 


4.5 


15.6 


8.6 


70.4 


4 


12 


8.5 


68.4 


3.5 


9 


8.4 


66.5 


3 


6.55 


8.3 


64.6 


2.5 


4.6 


8.2 


62.7 


2 


3.1 


8.1 


60.9 


1.5 


2.0 


8.0 


59.1 


1 


1.2 


7.9 


57.4 









•To obtain absolute luminous reflectance, multiply values given by 0.974. 



The Munsell notation for any color is written in this order: 

hue, value/chroma 
The most common form of notation includes letters and whole numbers 
for hue, and whole numbers for value and chroma: 
5R 4/10 is read "five red, four-ten." 

Examination of Fig. 4-4 reveals that when compared with 5R 4/10, 
4R 4/10 would be more purple 

5R 5/10 would be lighter (have higher luminous reflectance) 
5R 4/9 would be more neutral (gray) . 
For greater precision, decimals may be added : 

5.1R 4.2/10.3 would be slightly more yellow, lighter, and more chromatic 
than 5R 4/10. 

The hue letters and decimals may be avoided by using the 100-step hue 
scale shown in Fig. 4-4: 



COLOR 



4-9 



NAME 


SYMBOLS 


RED 


5 


R 


YELLOW- RED 


15 


YR 


YELLOW 


25 


Y 


GREEN-YELLOW 


35 


GY 


GREEN 


45 


Y 


BLUE-GREEN 


55 


BG 


BLUE 


65 


B 


PURPLE-BLUE 


75 


PB 


PURPLE 


85 


P 


RED-PURPLE 


95 


RP 



WHITE 




DIAGRAMMATIC VIEW 



NAME 


SYMBOLS 


YELLOW 


1 

2 
3 


IY 
2Y 
3Y 


ORANGE 


4 

5 
6 


10 
20 
30 


RED 


7 
8 
9 


1 R 
2R 
3R 


PURPLE 


10 
II 
12 


IP- 
2P| 
3P- 


ULTRA- 
MARINE BLUE 


13 
14 
15 


1 UB 
2UB 
3UB 


TURQUOISE 


16 
17 
16 


IT 
2T 
3T 


SEA GREEN 


19 
20 
21 


1 SG 
2SG 
3SG 


LEAF GREEN 


22 
23 
24 


1 LG 
2LG 
3LG 



MUNSELL 




FIG. 4-4. Common forms of Munsell and Ostwald color solids showing notation 
scales by which colors are designated according to their position in the solid. 16 



5 4/10 is read "five, four-ten" and equals 5R 4/10. 

95 4/10 is read "ninety-five, four-ten" and equals 5RP 4/10 read "five 
red-purple, four-ten." 

Collections of carefully prepared and standardized color chips may be 
obtained in several different forms from the Munsell Color Company, Inc., 
10 East Franklin Street, Baltimore 2, Maryland. Neither standard library 
nor pocket editions include the high-value illuminating-engineer's chips 



4-10 I E S LIGHTING HANDBOOK 

(higher than 8/). However, standardized chips which include high values 
of neutral grays, low chroma reds, yellows, greens, blues, and purples are 
mounted in the pocket-size folder (Fig. 4-5), which has been developed 
especially for illuminating engineers. The chips in the folder are arranged 
for convenient comparison with surface colors. With practice in the use 
of this chart, value may be estimated rather accurately and converted to 
luminous reflectance by means of the scales provided. Inexpensive papers 
in colors designated in Munsell notation, suitable for everyday use though 
not sufficiently uniform for standards, are available. 





FIG. 4-5. Munsell chart, pierced for easy com- 
parison with surface colors, permits quick estimate 
of luminous reflectance. 

Luminous reflectance for the neutral grays, which are nonselective, is 
the same for all illuminants, but for colors of high chroma, it depends upon 
the illuminant. The reflectance of a yellow surface will be higher under a 
yellow illuminant than under a blue illuminant, and so on. Reflectances 
which may be expected for several colors of high chroma under different 
illuminants are given on page 164, Humiliating Engineering, March 1945. 

Ostwald system. The Ostwald system of color order is presented in the 
Jacobson Color Harmony Manual, obtainable from the Container Corpora- 
tion of America,. Inc., Ill West Washington Street, Chicago 2, Illinois. 
In this system a color is designated according to its white, black, and "full- 
color" content by means of a letter notation which signifies the position 
of the color in the Ostwald color solid (Fig. 4-4) . 

The notation for a color is written in the form : 

ie8, which is read: "i, e, eight." 

This specifies a pink or pastel red. Examination of Fig. 4-4 reveals that: 



COLOR 4-11 

ie7 would be more orange 

ie9 more purple 

he8 would be less pure (more white) 

ke8 more pure (less white) 

id8 would be more pure (less black) 

if8 less pure (more black) 

ha8 would be lighter (higher luminous reflectance) 

kf8 would be darker (lower luminous reflectance) 
The solid is divided logarithmically along its vertical axis according to 
the Weber- Fechner law of equivalent sensation. Absolute white (luminous 
reflectance 100 per cent) is at the top of the scale and absolute black is at 
the bottom. It is also divided angularly into twenty-four "full-color" 
wedges, each of these represented by an equilateral triangle in a vertical 
plane through the axis covering an area of constant dominant wavelength. 
Colors located in lines parallel to the vertical axis (isochromes) have 
constant purity ; colors located in lines parallel to the bottom of the triangle 
(isotints) have constant white content; and colors located in lines parallel 
to the top of the wedge (isotones) have constant black content. 

If the reflectance of any two or more Ostwald colors is equal, it is the 
result of chance rather than of planning. However, I.C.I, (x, y) co- 
ordinates for each chip in the Jacobson manual have been determined and 
the Ostwald notations for this set of chips may be transposed through the 
I.C.I, co-ordinates to Munsell notation or any other notation for which 
I.C.I, data are available. These I.C.I, co-ordinates are not applicable to 
any set of Ostwald chips 15 except those of the Jacobson manual. 

Basic Systems of Color Specification 

I.C.I, system. The I.C.I, standards for colorimetry consist of data 
representative of a normal (standard) observer and three standard illumi- 
nants (A, B, and C). The conditions of illuminating and viewing the test 
sample are specified as 45 degrees and 90 degrees respectively. In this 
system color is expressed in terms of three primaries. 16 

Results of any spectrophotometric measurement may be reduced to the 
terms of the I.C.I, observer and co-ordinate system. In I.C.I, form, the 
data are expressed as the absolute (X, Y, Z) and fractional (x, y, z) amounts 

of each primary which, for the standard observer, match a given sample 

y 
under a given illuminant. The fractional values x = ^ — : — tz — : — - and 

Y 

V ~ y I v , y are called the trichromatic coefficients of a color. The 

value of luminous reflectance or transmittance (r or t) equals the Y value 
which carries all the luminosity. To avoid the use of negative numbers in 
specifications, the three primaries have been assigned mathematical charac- 
teristics which cannot be reproduced in any physical form, such as red, 
green, or blue lights. However, since the specifications may be used con- 
veniently and the primaries need never be used, the theoretical character of 
the latter is not a practical obstacle. 



4-12 



I E S LIGHTING HANDBOOK 



In Appendix Table A-ll, page A-26, the characteristics of the standard 
observer (Table 1-3, page 1-4) are combined with data for several light 
sources, ready for computational use in the manner indicated on page A-24. 

Dominant wavelength, purity, and luminous reflectance. Dominant wave- 
length and purity are quantities which are more suggestive of the appear- 
ance of a color than the I.C.I, specifications, from which they may be deter- 
mined in the manner indicated on page 4-14. They may also be found 
by direct measurement. 17 They specify the chromaticity of a color, and 
Figs. 4-6, 4-7, and 4-8 are chromaticity diagrams. 



0.52 MICRON 



'•"Op.53 



DOMINANT WAVELENGTH Or 
X = 0.382, LJ = 0.542 WITH 
RESPECT TO: 

(S 2 ): 0.553 MICRON 

PURITY a/b-50°/o 



(S,): 0.590 MICRON 
^ PURITY C/d = 47°/o 




FIG. 4-6. Locus of spectrum colors plotted on a chromaticity dia- 
gram showing method of obtaining dominant wavelength and purity 
for different samples under different illuminants. 



To obtain values by direct measurement, 17 a mixture is made of the 
amount of spectrum light of a homogeneous nature (single wavelength) and 
the amount of heterogeneous equal energy (neutral) light needed to match 
a given sample. The tristimulus coefficients for the equal energy spec- 
trum are given in Appendix Table A-15, page A-34. The wavelength of 
the monochromatic spectrum light needed for a match is the dominant 
wavelength of the sample. The proportion of the spectrum light (per cent) 
in the mixture needed for a match under a given illuminant is the purity 



COLOR 



4-13 



ABBOT MEAN NOON SUN 



MACBETH 6,800' 
PLANCKIAN 7,000° K 
MACBETH 7,500 



)»,<■*, J*t^4 GIBS0N V^ (0.1+0.9) 
::, > \ /VG I BSON >/ A 4 (0.15+0.85) _ 

-K.4FLL 





CARBON ARC • 
\ 



FLUORESCENT 7,650 K 
GIBSON YyA (0.2+0.8) 



GIBSON l/^ 4 (0.3 + 0.7) 



200MIREDS 



100 MIREDS 



-MERCURY LINES 
(OF FLUORESCENT 
+ BLUE 7,650°k)«<v\ " .'. . s 

©*' ^GIBSON Y£ (I.O + O) 



FIG. 4-7. Section of expanded scale chromaticity diagram showing 
Planckian locus and isotemperature lines for determining nearest color 
temperature. (Ilium Eng., March, 1941) 



of the sample (spectrum plus equal [neutral] energy = 100 per cent). 
Luminous reflectance may be determined by any method of heterochromatic 
photometry. 

Color temperature. Color temperature describes the chromaticity of a 
completely radiating (blackbody) source and is widely used in illumination 
work. Such a body is black at room temperature (when it does not radiate 
any visible energy), red when heated to a temperature within 800 K to 
900 K, j r ellow at about 3,000 K, white (neutral) at a temperature of 5,000 K, 
weak blue at a temperature between 8,000 K and 10,000 K, and a more 
brilliant blue, such as sky blue, when heated to a temperature of 60,000 K 
to 100,000 K. The characteristics of a blackbody at different tempera- 
tures are defined by Planck's law. (See page 1-8.) The locus of black- 
body chromaticity on the diagram shown in Fig. 4-6 is known as the 
Planckian locus. 

Any chromaticity represented by a point on this locus may be specified 
by color temperature. Color temperature should not be used to specify 
a chromaticity that does not lie on the Planckian locus. However, what is 
called the nearest or correlated color temperature is sometimes of interest, 
and has been defined. 18 The loci of isotemperature lines that may be used 
as an approximation to obtain a reading on the diagram of the nearest color 
temperature are shown in Fig. 4-7. 

Equal color differences are more nearly expressed by equal steps of recip- 
rocal color temperature than by equal steps of color temperature itself. 



4-14 



I E S LIGHTING HANDBOOK 



A difference of one microreciprocal degree 



CT 



X 10 5 = 1 mired (pro- 



nounced my-red) 



, indicates approximately the same color difference 



anywhere on the color temperature scale above 1,800 K; whereas 1 mired 
is derived from a difference that varies in color temperature from about 
4 degrees at 1,800 K, 25 degrees at 5,000 K, 46 degrees at 6,700 K, to 100 
degrees at 10,000 K. 

Color temperature is a specification of chromaticity only, and has nothing 
to do with the energy distribution of an illuminant. The chromaticities of 
many "daylight" lamps plot very close to the Planckian locus, as shown in 
Fig. 4-7. Their color may be specified in terms of nearest color temperature. 
However, this specification gives no information about their spectral energy 
distribution and must be used cautiously. (See Fig. 4-10.) 

Correlation between Methods of Color Designation and Specification 

The various forms of color designation and specification are frequently 
encountered under circumstances which require or make desirable the 
conversion of the notation or specification for a color from one system to 
another, just as dimensions in feet are often converted to dimensions in 
meters. 19 

I.C.I, co-ordinates to or from dominant wavelength and purity. Plot the 
spectrum locus on an x — y diagram and plot the location of the illuminant 
as in Fig. 4-6. Draw straight lines from the illuminant point to the spec- 
trum locus at regular intervals (0.001, 0.01, or 0.1 micron). All colors 
whose x — y co-ordinates fall on one of these lines have the dominant 
wavelength indicated by the intersection of the line with the spectrum locus. 
Their purity is determined by dividing their distance from the illuminant 
point by the distance along the same line from the illuminant point to the 
spectum locus. One hundred per cent purity is at the spectrum locus; 
colors of 50 per cent purity fall halfway between the illuminant point and 
the spectrum locus, per cent purity is at the illuminant. Reflectance 
equals the Y value of the I.C.I, co-ordinates, and may be obtained by 
heterochromatic photometry. 

Any (x — y) specification is accurate only for the illuminant for which 
it is calculated. The dominant wavelength and purity corresponding to 
any x — y specification also depend on the illumination. For example, 
x = 0.41, y = 0.40 is a blue — dominant wavelength approximately 0.492 
micron and purity 10 per cent when referred to illuminant A; but the same 
(x — y) point when referred to illuminant C is a yellow — dominant wave- 
length 0.590 micron and purity 50 per cent. 

I.C.I, co-ordinates to or from Munsell notation. A complete set of charts 
of the type shown in Fig. 4-8 has been prepared by a subcommittee of the 
Colorimetry Committee of the Optical Society of America. Instructions 
for converting from I.C.I, to Munsell notation and vice versa are included. 20 




FIG. 4-8. Conversions between I.C.I. , Munsell, and dominant wavelength nota- 
tions may be made directly on charts such as these. 20 (A) Constant chroma loci 
for standard chromas at value levels 1 through 9. (B) Constant hue loci for standard 
hues at value levels 1 through 9. 



4-16 



I E S LIGHTING HANDBOOK 



I.C.I, co-ordinates from spectrophotometry curves. Although it is not 
possible to construct a spectrophotometric curve from a color specification 
in I.C.I, co-ordinates or other shorthand notation, I.C.I, co-ordinates x, y 

and Y may be obtained from spec- 
trophotometric curves. The example 
given in the Appendix on page A-24 
illustrates the procedure 21 for making 
the necessary computations for a deep 
red reflecting surface whose spectral 
reflectance curve is given in Fig. 4-9. 
Solutions by both the weighted ordi- 
nate and selected ordinate methods are 
explained and Appendix Table A-13 on 
page A-28 gives selected ordinates for 
illuminants A, B, and C. A mechani- 
cal integrator, by means of which much 
of the numerical work of the selected 
ordinate method may be eliminated, is 
a time-saving tool. 





































J 











0.76 



0.40 0.50 0.60 0.70 

WAVELENGTH IN MICRONS 

FIG. 4-9. Spectral reflectance 
curve for a vivid red surface Munsell 
R4/14. 1 micron = 10,000 angstroms 
= 1/10,000 centimeter. 



Color Harmony in Design 

Many theories of color aesthetics have been published. Most of these 
are expressed in terms of one or another of the numerous systems of 
surface color designation. To a considerable extent, they represent codifi- 
cations of artistic taste and experience. Although many of these differ 
greatly in many details, a few general principles have been expressed 
repeatedly. 14 . 15 - 22 . 23 - 24 

Both the purpose of a color scheme — whether in a factory or night club, 
on a machine or on a stage — and the amount, quality, and distribution of 
illumination that is to be available, should be known before colors are 
selected. 

Composition and design are always of paramount importance. A good 
color combination will be most pleasing when used in a good design, and 
an excellent design can make almost any combination of colors acceptable. 
Consequently, it is possible to find or create exceptions to all "rules" of 
color harmony. 

Consistency of both design and color can be maintained without mon- 
otony. It is possible to use a single hue exclusively if variations of value 
(luminous reflectance) and chroma are employed in a design that provides 
interest, accent, and variety. The use of one or more hues contrasting 
with the dominant hue is the most common method of avoiding monotony. 

Contrasting hues of high chroma are most effective when used in small 
areas. Light colors (high reflectance) are effective as accents in dark sur- 
roundings (prevalently low reflectance), and dark colors are effective for 
variety and interest in light surroundings. Contrasting hues may be, but 
need not be, complementary. . 



COLOR 4-17 

Triads of hues, two of which are related but not too nearly alike and the 
third of which is approximately complementary to the average of the pair, 
are often effective. The pair may be used together to establish the dom- 
inant hue, or they may be used for accent and variety. It is usually best 
to treat the neighboring hues of a triad in a similar manner, assigning ap- 
proximately equal areas to each and using equal ranges of value and chroma. 

All principles, such as the preceeding examples, may be violated success- 
fully by clever designers, but greater care and ingenuity are necessary in 
breaking the rules than in observing them. 

Psychological and physiological sensations attributed to color. In almost 
every discussion of the aesthetic factor in color schemes some correlation 
between color and nonvisual sensations is suggested. The most popular 
association consistently emphasized by artists is the supposed relationship 
of the red colors (red purple, red, orange, and yellow) with warmth and the 
blue colors (bluish purple, blue, and blue-green) with lack of warmth. 
This appears to have no foundation in fact. 25 

Color Selection, Grading, Matching, Control, and Tolerances 

No factor is more important in problems of color selection, matching, 
control, and grading than the spectral distribution (color) of the illumina- 
tion on objects under observation. 

Color selection. If the problem is one of simple selection, as for example 
that faced by the housewife about to choose from an assortment of meat, 
at the meat dealer's, or of fruit or vegetables at the grocer's, or from an 
assortment of dress and upholstery fabrics, paints, or wallpapers at a de- 
partment store; the decision will be based on the appearance of the object 
on display and upon the customer's estimate of its probable appearance 
under the conditions most likely to be encountered in use. The conditions 
of display and use differ more often than they coincide. This is particu- 
larly true of the illumination. 

If spectrophotometric facilities are not available, color matches satisfac- 
tory for many purposes may usually be assured by the simple expedient of 
checking the match under each of two illuminants of complementary color, 
red and green, for example, or yellow and blue. For many simple matching 
problems a low wattage incandescent lamp and a blue or daylight fluorescent 
lamp are adequate. 

A perfect match under all conditions will be obtained by matching spec- 
trophotometric curves of the type shown in Figs. 4-9 and 4-10. Two 
surfaces having identical curves are in general identical in color to each 
other under all conditions although if their surface textures are not the same 
(smooth paint and rough textiles, for example), their appearance may vary 
slightly depending on the angle from which they are illuminated and viewed. 

Color grading and matching. The market value of many things — raw 
cotton, tobacco, fruit, vegetables, furs, textiles, and so forth — varies with 
their colors over a very wide range. In some instances such products are 
accepted or rejected on the basis of color specifications or standards. They 



4-18 



I E S LIGHTING HANDBOOK 



may be separated according to nearly imperceptible color differences into 
a number of "standard" grades each of which may have a different market 
value. 

It is frequently necessary to obtain a "commercial match" between 
physical samples (supplied for purposes of specification) and production 
samples (selected for purposes of production quality control). The 
test procedures under the specifications should be so defined that experi- 
enced persons consistently and independently assign the same grades and 
make the same matches. 



o 
< 















c 


/ D 












A AND B 

























1.40 0.50 060 0.70 

WAVELENGTH IN MICRONS 



FIG. 4-10. Spectral reflectance and 
transmittance curves reveal slight dif- 
ferences between samples which may 
not be detected by visual observation 
under ordinary light sources. To a 
normal observer, samples A and B 
seem to match as do C and D, when 
viewed under incandescent lamps; C 
and D are pink but of higher value 
(luminous reflectance) than A and B. 
While the spectral reflectance curves 
prove the physical similarity of A and 
B, they reveal a difference between C 
and D. A and B will match under 
any conditions, but C and D will not 
match if the illumination contains a 
high percentage of blue energy in the 
region 0.4-0.5 micron. 



Color control in a lighting installation. The artist, architect, and illum- 
inating engineer, after agreeing on a design having suitable decorative 
qualities and which at the same time will provide the proper quantity and 
quality of illumination, have the problem of transferring their plans to the 
room in question. This must be done by specifying to the contractor and 
builder, as well as to the furniture, wall covering, drapery, and paint manu- 
facturers, what materials will be acceptable from a color standpoint. The 
fundamental problem is similar to that worked out by the retail packaging 
experts. 

Color control in production. There are many reasons for requiring ac- 
curacy and precision in the control of the color of surface coatings, such as 
printing inks and industrial finishes. Perhaps the most important reason 
concerns the demands made by the buyers of retail consumer goods, and 
the quality significance they attach to the color of articles. 

The use of color control usually has three objectives. The first objective 
is that a satisfactory match for the desired color should be obtained with 
the type of coating formulation which will be used in production. The 
second objective is that the standard color achieved as a result of the first 
should be maintained during the first mass production of the material. 
The third objective requires that subsequent mass productions of the ma- 
terial have the same color as the first mass production. For those articles 
which are in almost continuous mass production, such as cigarette contain- 
ers where the production for a single brand may be several million packages 



COLOR 4-19 

a day, the last two are the same. An excellent description of the color 
control procedure applied in the packaging field was given by Granville 
in Illuminating Engineering in December, 1944. 23 

Spectrophotometry control. The type of color standardization and control 
provided by spectrophotometric measurements has increased in use. Such 
measurements provide a permanent record which can be converted into a 
color specification. The application of the spectrophotometer to the 
problem of color standardization for production control purposes is almost 
universally recognized as the best approach though not the onty one. 21 - 27 

Color tolerances. Tolerances are generally thought of in terms of color 
differences; however, color tolerances should be considered also on the basis 
of what can be done in production. One type of tolerance limit is caused 
by production difficulties. Once selected, tolerances can be specified 
spectrophotometrically, and tolerance limits can be prepared for visual 
comparison on a production basis. 28 

Illuminants for Color Work 

Surface colors which match in one quality of illumination but do not 
match in another invariably result from unlike spectral reflectance curves. 
Conversely a spectral energy match is, in general, required of any illu- 
minant intended as a substitute for another whenever colors are to be exam- 
ined critically. 

Any change in the characteristic spectral curve of illuminants used as 
substitutes for each other will cause differences in the appearance of objects 
seen under them. The amount of color constancy or color change will 
depend on the spectral distribution of the illuminant and on the spectral 
reflectance of the object. If the spectral reflectance of an object is non- 
selective, that is, equal in all parts of the spectrum (as for nonselective 
whites, blacks, and grays) , then there will be little difference in appearance 
under two illuminants that have the same color temperature but do not 
have similar spectral energy distributions. 

Artificial daylighting. Specifications for the best artificial daylighting 
for use in grading include: a large source of relatively low brightness; dupli- 
cation of color of moderately overcast north sky; illumination of at least 
75 footcandles for inspecting light colors, more for dark colors. 

The color specification for an artificial daylight illuminant should be 
aimed at the best obtainable duplicate of preferred natural daylight condi- 
tions. Most commercial grading is done under natural daylight and for 
such grading the results of classification under artificial and natural day- 
lighting should agree. Also, it takes years of experience to make a good 
classer, grader, or inspector, and an accurate memory of color standards is 
a necessity. Any great change in illumination requires that classers make 
adjustments in their memory of standards. The greater the change, the 
more difficult this becomes. If artificial illuminants are to be preferred 
rather than be merely tolerated for color grading, psychological as well as 
physical standards must be maintained, 



4-20 I E S LIGHTING HANDBOOK 

Inspection for suitability of color of materials to be used in daylight (as 
by a customer in a retail store) requires only an approximate duplication 
of the spectral-energy distribution of natural daylight, because large ob- 
ject-color variations are tolerable. The normal eye adapts readily to 
rather large changes in the ehromaticity of an illuminant so that the 
apparent colors of objects remain approximately constant. 

Color grading of a group of material samples known to have similar 
spectral-reflectance characteristics may require close duplication of the 
spectral-energy distribution of daylight. This use, however, differs from 
the other uses listed because large departures from the spectral-energy 
distribution of natural daylight are allowable as long as they yield in 
undiminished amount the object-color differences characteristic of daylight 
inspection. Whenever, as is frequently true, the artificial illuminant mag- 
nifies the characteristic differences so that they may more easily be detected, 
departures from the spectral-energy distribution of natural daylight are 
desirable. If yellow samples are to be examined, an illuminant rich in 
energy in the blue portion of the spectrum, where the spectral reflectances 
of yellow samples are apt to differ most widely, will enable an observer to 
discriminate differences more easily than when using an illuminant deficient 
in the blue portion of the spectrum. When blue samples are to be exam- 
ined, the reverse is true; i.e., an illuminant rich in energy in the yellow 
portion of the spectrum will facilitate discrimination. It should be remem- 
bered that while differences may be revealed by such a method the average 
daylight appearance of the samples will not necessarily be revealed. If 
the observer is an experienced color-grader, duplication of the natural 
daylight ehromaticity familiar to him will permit him to take full advantage 
of his previous experience and will make conversion to the new conditions 
much less difficult. 29 

A practical application of this general method is used in dye houses. 
When samples are to be matched they are viewed under two illuminants 
selected at or near the extremes of daylight color temperatures. 

Preference of textile color matchers. Data obtained by an Inter-Society 
Color Council Committee indicates that the footcandle and color tempera- 
ture combinations of natural daylight preferred by textile color matchers 
are as shown in Fig. 4-11 A. At 100 footcandles, the minimum color tem- 
perature preferred is close to 7,500 degrees, and the maximum is above 
25,000 degrees. The preferred color temperature may drop to 5,700 de- 
grees for values of 300 or more footcandles. 31 

Skylight design for natural daylight. The government-type skjdight 
(Fig. 4-1 IB) used in many commercial and government cotton-classing 
rooms was developed for the United States Department of Agriculture. 30 
The glass faces due north and its departure from the vertical changes with 
the latitude to exclude direct sunlight. The length varies from 30 to 90 
feet, the longest skylight being the most satisfactory. 

While such natural daylighting of color grading rooms has been success- 
ful, many rooms cannot be placed on a top floor, or be so oriented that a 
long north skylight is possible. Even when light from a north window has 
been used satisfactorily for years, taller buildings built near by may shut 



COLOR 



4-21 



5,000 
500 



COLOR TEMPERATURE IN DEGREES 
6 250 8,333 12.500 25,000 



O 400 
■$■ m 

7 2 300 

is 

<o 

ZO 200 























IS£S? 
































....... 








PREFERRED CONDITIONS: 























(A) 



200 ISO 160 140 120 100 80 60 40 20 

MICRO RECIPROCAL DEGREES (MIREDS) 




PTG.4-11A. Tests conducted under the direction of the Intersociety Color Council 
show the characteristics of preferred daylight illumination conditions for color 
matching, grading, and classing. B. Government type skylight; glass faces due 
north running east and west; all reflecting surfaces are finished in neutral white 
or gray. 



off the light or change its color by reflection from colored walls. The 
weather may be bad during the peak of a classing season, and extra work 
may pile up that cannot be completed within the few hours of good light 
available each day. 



4-22 I E S LIGHTING HANDBOOK 

Artificial skylight for preferred daylight color rendition. The lamp-and- 
filter unit shown in Fig. 4-12 approximates 7,500 degrees Kelvin color 
temperature and has a spectral distribution similar to daylight of that color 
temperature. It was developed for cotton classification. On a run of 
over 2,000 test classifications it was found that a somewhat greater con- 
sistency of classification was attained under the uniform quantity and 
quality of illumination provided by this artificial source than under natural 
daylight, and no significant differences in classification have been noted. 
Cotton classing groups which now use this unit are satisfied with the results 
obtained as are many other grading and inspecting groups which have 
adopted it for their work. 






FIG. 4-12. Artificial skylight used at the Division of Cotton Marketing, U. S. 
Department of Agriculture, for color grading of agricultural products. Fifteen 
lamps and filters are mounted behind a diffusing glass panel in a ventilated en- 
closure finished with heat absorbing white paint. 

A similar type of unit approximating I.C.I, illuminant C in color tem- 
perature and several other "dajdight" sources such as the high-temperature 
carbon arc, carbon dioxide and fluorescent tubes, and so forth were consid- 
ered before the 7,500-degree color temperature was recommended, but they 
were found less satisfactory. 30 

Figure 4-13 includes curves of relative spectral energy distribution for a 
number of actual and theoretical illuminants that have been considered as 
daylight substitutes. 

Imperceptible supplementation of natural daylight requires careful dupli- 
cation of the particular phase of natural daylight supplemented. Color 
matching of materials to be used in daylight (in dyeing textiles, and so on) ; 
color inspection of materials to be used in daylight for conformity, within 
a specified tolerance, to a given color standard; and photographic sensitom- 
etry all require close duplication of the spectral-energy distribution of 
natural daylight in the illumination specified for the work. 

Color photography is in all essential respects analogous to color vision. 
Illuminants intended as substitutes for, or to supplement daylight for 
color photography should have very nearly the same spectral distribution 
as the illuminant replaced. Neither color temperature nor a visual color 
match is a sufficient specification for illuminants used in color photog- 
raphy. 32 (See Section 14.) 



COLOR 



4-23 



3. AV. DAYLIGHT 
-4. AV. SUNLIGHT 



1. AV. DAYLIGHT , , RRnTl 

2. NOON SUN ( ABB0T) 



(LUCKIESH) 




.C. I. ILLUMINANTS 




- 6,500 K 



PLANCKIAN 
DISTRIBUTIONS 




0.7 0.4 0.5 0.6 0.7 0.4 

WAVELENGTH IN MICRONS 



1 micron = 10,000 angstroms = 1/10,000 centimeter 
FIG. 4-13. Spectral energy distribution curves for illuminants sometimes con- 
sidered as substitutes for natural daylight. 



Paint mixing. When a painted surface of a certain color is desired, it 
is often possible to select satisfactory colors from the stock samples found 
on manufacturers' color cards. However, if the manufacturers' stocks do 
not include the desired color, and the painter wishes to mix his colors, 
mixing guides are available which suggest the proportion of various raw 
ingredients for each of the paint chips included. (See page 4-6.) 

To be sure of an exact match with the sample selected, it is necessary to 
use the specific raw materials and proportions recommended and to check 
the match using the illumination under which it will be observed. In 
mixing small quantities (a pint or less) it is sometimes difficult to measure 
accurately the relatively minute quantities of certain raw materials re- 
quired and for this and other reasons it is often difficult to make a close 
match. This is particularly true of high value, low chroma (pastel) colors. 33 



4-24 I E S LIGHTING HANDBOOK 

Spectrophotometry 

Spectrophotometry is the measurement of spectral reflectance and trans- 
mittance. 21 Colorimetric data may be obtained from spectrophotometric 
measurements which have been converted to I.C.I, notation. (See page 
4-16.) 

The modes of illumination and collection differ in various spectrophotome- 
ters. Since the results depend on the slit width, the illumination and col- 
lection geometry, and the calibration, these should be reported clearly with 
each spectrophotometric curve. 

Gloss has a marked effect on the object color perceived but gloss itself 
is best measured with instruments such as a goniophotometer. (See Sec- 
tion 5.) The color corresponding to any particular mode of illumination 
and observation can, in principle, be determined from separate and inde- 
pendent determinations of the color and gloss of any sample. 

In a spectrophotometer a spectroscope disperses the light into its com- 
ponents and a photometer measures the amount of light of each wavelength 
transmitted or reflected by a sample, by comparing the unknown quantity 
with a standard. In early models, the judgment of match was made by 
eye. This was time-consuming, even if measurements were made only at 
0.02- or 0.04-micron wavelength intervals. Also, if a tungsten filament 
lamp is used as the light source in a visual instrument, it provides so little 
light in the blue end of the spectrum that it is very difficult to make either 
precise or accurate judgments. 

However, photoelectric spectrophotometers are not as greatly handi- 
capped in this way and several are now available in Avhich the illumination 
is satisfactorily provided by a tungsten lamp chosen because it is con- 
venient and emits a continuous spectrum. The latter is a usual require- 
ment in spectrophotometry for if the illumination falling on a sample 
surface has no energy in some part of its spectrum, then no energy can be 
reflected or transmitted for measurement in that part of the spectrum, no 
matter how much a sample may be able to reflect or transmit in that 
region. 

Present commercial models of the best-known automatic recording in- 
strument, shown in Fig. 4-14A, illuminate the sample about 6 degrees from 
the normal, and view it diffusely by gathering light from the white interior 
surface of a hollow sphere. The results correspond to the appearance of 
the sample when held perpendicular to the line of sight in completely 
diffused indirect lighting. 34 ' 36 A manual type of instrument is shown in 
Fig. 4-14B. 35 ' 36 

The optics of any spectrophotometer must be designed to utilize as much 
as possible of the available energy so that narrow slit widths may be used 
in making measurements. A good spectrophotometer source must emit 
enough energy in all portions of the spectrum so that measurements may 
be made with slit widths that admit light from bands 0.01 micron or less 
in width. 



COLOR 



4-25 




condenser lens 
j^Qlamp 



COLLIMATOR LENS 



FIG. 4-14. Typical photoelectric spectrophotometers, (A) automatic recording 
type, (B) manual type. 



Incidence at substantially 45 degrees from the normal to the surface 
and collection or observation of the light reflected perpendicular to the 
surface were the conditions recommended by the I.C.I, in 1931, and these 
conditions are realized approximately in some instruments. However, 
this condition was omitted from ASA Z44-1942 (page 32), since agreement 
on the best viewing and illuminating geometry had not been reached. 
Illumination substantially perpendicular to the surface and collection of 
substantially all the reflected energy represent the condition most com- 
monly used because of its efficiency in photoelectric instruments and 
because objects made with the same colorants but having markedly dif- 
ferent surface characteristics (e.g., dull and glossy) give nearly the same 
results under this condition. In this manner, the color measurement can 
be made nearly independent of gloss. 

Spectrophotometric measurements on a sample — provided there is 
enough light to make precise measurements, and provided wavelength 
bands are equally narrow — -will be the same regardless of the illuminant as 



4-26 



I E S LIGHTING HANDBOOK 




0.44 0.52 0-60 0.68 0.76 12 3 4 

WAVELENGTH IN MICRONS 




0.6 0.7 0.4 0.5 0.6 0.7 0.4 0.5 0.6 0.1 

WAVELENGTH IN MICRONS 

1 micron = 10,000 angstroms = 1/10,000 centimeter 

FIG. 4-15. Spectral transmittance curves for a number of ground and polished 
samples of various melts* of glass (top) . (below) Spectral reflectance curves for vari- 
ous painted surfaces. The luminous reflectance in per cent for incandescent lamps 
is indicated by the left hand figures. The right hand figures indicate luminous 
reflectance for daylight fluorescent lamps. 

long as the illuminant used emits energy of all wavelengths. A color-blind 
observer using the direct visual comparison type of spectrophotometer may 
make measurements quite as accurately as an observer with normal color 
vision, since all that is necessary is an accurate judgement of brightness 
equality. 

An automatic recording spectrophotometer may produce a continuous 

* Figures on curves refer to standard melts of the Corning Glass Works. Transmittance decreases rapidly 
as the sample thickness increases and vice versa. 



COLOR 4-27 

curve or a table of transmittance values at specified wavelength intervals 
(usually 0.02 micron). 

Figure 4-15 shows spectral reflectance and transmittance curves obtained 
with a spectrophotometer for a number of different samples of common 
materials. 

Colorimetry 

Color and the color properties of objects may be measured in many ways, 
all of which involve, either directly or indirect^, visual comparisons of a 
sample with optical combinations of measured quantities of several (usually 
three) fixed or physically specifiable qualities of light. 37 

Direct colorimetry is simpler than indirect but is subject to errors and 
uncertainties arising from the nonuniform spectral sensitivity of any ob- 
server and individual differences of considerable and variable magnitude 
between observers. In some applications, such as product inspection and 
quality control, direct visual comparison is preferable because of the flexi- 
bility and simplicity of the procedure. 

Indirect colorimetry utilizes spectral distribution data for sources, spectro- 
photometric data for surfaces, and standard colorimetric data representa- 
tive of a normal observer. Standards and tolerances for inspection and 
control are best established and maintained by spectrophotometry and 
indirect color measurement. Only by this method can long-term changes 
resulting from fading, drift, loss, or destruction of the standard, be avoided. 

Color mixture. Both direct and indirect methods of color measurement 
are based on the fact that a color match can be established between optical 
mixtures of any sample color and variable amounts of three standard colors. 
In some cases, one of the standard components must be combined optically 
with the sample light in order to match some combination of the other two 
standards and the amount of the standard mixed with the sample is then 
recorded as a negative quantity. In rare instances, two of the standards 
need to be mixed optically with the sample light in order to match the third 
standard and the amounts of the two standards mixed with the sample are 
both recorded as negative quantities. Curve a in Fig. 4-164 shows the 
number of lumens (spectrally pure red primary, wavelength 0.65 micron) 
required to establish a match with one watt of spectrally pure energy at 
each indicated wavelength, when two other spectrally pure components, 
wavelengths 0.538 micron and 0.425 micron, are used (in the proportions indi- 
cated in curves b and c) as the other primaries. Curve b in Fig. 4-164. 
indicates the number of lumens of the yellowish green primary (0.538 micron) 
required for these color matches. Curve c in Fig. 4-164. indicates the 
required number of lumens of the bluish purple primary (0.425 micron). 

Photoelectric colorimeters are frequently described, but since no photo- 
electric cells, nor any photocell-filter combinations, have yet been de- 
veloped with the color response of the human eye, none are entirely satis- 
factory. A few have been built that approach the desired accuracy 
including the instruments built and used by Barnes, 38 and the Hunter 
instrument 39 widely used in the paint industry. 



4-28 



I E S LIGHTING HANDBOOK 



600 



500 




1<^ 



0.50, 0.55 0.60 0.65 0.70 
WAVELENGTH IN MICRONS 
(A) 



JE 0.8 



A 










1 

i 


\ 

\ 










I 


\ 










1 


\ 


y 




\ x 




1 


1 


/ 








1 


\ 


/ 
/ 
/ 


/ \ 

/ \ 






l 


\ 


/ 

; 
/ t 




\ \ 
\ \ 

\ \ 




l r 


\ ) 






\ \ 




If 


\ / 


V 




\ 

\ 






•\ 


«/^-», 


— 


\ 


y,\. 



0.40 0.45 0.50 0.55 0.60 0.65 0.70 

WAVELENGTH IN MICRONS 

IB) 



1 micron = 10,000 angstroms = 1/10,000 centimeter 

FIG. 4-16/1. (a) Lumens of 0.65 micron red component in mixture with 0.538 
micron (yellowish green), and 0.425 micron (bluish purple), which matches color of 
one watt of energy at each spectrum wavelength; (6) lumens of 0.538 micron (yellow- 
ish green); (c) lumens of 0.425 micron (bluish purple). B. Standard I.C.I, color 
mixture data obtained by linear combination of a, b, and c. Y is identical to the 
standard relative luminosity curve. 



Empirical colorimeters employing the sub-tractive principle have been 
built for specific purposes : the Lovibond tintometer for use with Lovibond 
glasses, another designed by Judd for very precise measurement of small 
chromaticity differences, 37 and the Eastman color densitometer. There 
are others of the additive type, such as the disk colorimeter originally 
designed for use in the grading of agricultural products. 27 

Three-color colorimeters, which use spectrum components, have been 
described by Wright in reports of many research problems. 37 Other three- 
color colorimeters using filters, such as those designed by Guild and Donald- 
son, are used in England. Instruments have been described and built for 
the direct determination of dominant wavelength, but little or no commer- 
cial application has been made of this type. 

Color comparators. Two classes of instruments commonly called colorime- 
ters should be distinguished. The first is that just described. The other 
is employed principally in chemical analysis for determining concentrations 
of solutions, or for the empirical grading of samples according to color. 
These might better be called color comparators as they are not true meas- 
uring instruments. 

REFERENCES 

In addition to the numbered references listed below, a most comprehensive discussion of the technical 
aspects of color supplemented by a liberal tabulation of literature citations is the report of the Colorimetry 
Committee of the Optical Society of America. Chapters of this report have been published in the' Journal 
of the Optical Society of America as follows: 

Jones, L. A., "The Historical Background and Evolution of the Colorimetry Report," October, 1943. 

Chapter II. "The Concept of Color," October, 1943. 

Chapter V. "Physical Concepts: Radiant Energy and Its Measurement," Aprii, 1944. 

Chapter VI. "The Psychophysics of Color," May, 1944. 

Chapter VII. "Quantitative Data and Methods for Colorimetry," November, 1944. 

Chapter VIII. "Colorimeters and Color Standards," January, 1945. 



color 4-29 

1. Tang, K. Y., "Visual Performance Under Daylight, fnoandeseent, Mercury Vapor, and Their Mix- 
tures," Trans. Ilium. Eng. Soc, March, 1931. Ferree, C. E., Rand, G., Irwin, B., Luckiesh, M., Priest, I. G., 
Richards, H. C, and Troland, L. T., "A Color Symposium," Trans. Ilium. Eng. Soc, February, 1918. Ferree, 
C. E., and Rand, G., "Further Studies on the Effect of Composition of Light on Important Ocular Functions," 

Trans. Ilium. Eng. Soc, May, 1924. , "The Effect of Variation of Visual Angle, Intensity, and Composition 

of Light on Important Ocular Functions," Trans. Ilium. Eng. Soc, February, 1922. 

2. Brainerd, A. A., and Denning, M., "Improved Vision in Machine Tool Operations by Color Contrast," 
Ilium. Eng., December, 1941. 

3. Brainerd, A. A., and Massey, R. A., "Salvaging Waste Light for Victory," Ilium. Eng., December, 1942. 
Nelson, J.H., "Ideal Seeing Conditions," Brit. J. Ind. Med., October, 1945. 

4. Moon, P., "Wall Materials and Lighting," J. Optical Soc. Am., December, 1941. Seealso: 

Moon, P., "Optical Reflection Factors of Acoustical Materials," J. Optical. Soc Am., April, 1941. Moon, 
P., "Colors of Ceramic Tiles," J. Optical Soc. Am., July, 1941. Moon, P., "Reflection Factors of Floor Mate- 
rials," J. Optical Soc Am., April, 1942. Moon, P., "Reflection Factors of Some Materials used in School 
Rooms," J. Optical Soc. Am., April, 1942. Moon, P., "Colors of Furniture," J. Optical Soc. Am., May, 1942. 
Moon, P., "Interreflections in Rooms," J. Optical Soc Am., May, 1941. Paul, M. R., "The Effect of Weather- 
ing on the Reflection Factor of Surfacing Materials for Light Wells," Trans. Ilium. Eng. Soc, April, 1933. 

5. Nickerson, D., and Newhall, S. M., "Central Notations for ISCC-NBS Color Names," J. Optical Soc 
Am., September, 1941. 

6. Judd, D. B., "Color Systems and Their Inter- Relations," Ilium. Eng., March, 1941. 

7. Judd, D. B., and Kelly, K. L., "Method of Designating Colors," J. Research Nat. Bur. Standards, 
September, 1939. Kelly, K. L., "Color Designations for Lights," J. Optical Soc Am., November, 1943. 

8. Lovibond, J. W., "The Tintometer — A New Instrument for the Analysis, Synthesis, Matching, and 
Measurement of Colour," J. Soc Dyers and Colourists, Volume 3, 1887. , "On a New Method of Colour Anal- 
ysis by Means of the Tintometer," J. Soc Chem. hid., 1890. , Measurement of Light and Colour Sensations, 

George Gill & Sons, London, 1893. 

9. Three Monographs on Color: Color Chemistry, Color as Light, Color in Use, International Printing Ink 
Corporation, New York, 1935. 

10. Gibson, K. S., Harris, F. K., and Priest, I. G., "The Lovibond Color System, I. A Spectrophotometric 
Analysis of the Lovibond Glasses," Nat. Bur. Standards, Scientific Paper A r o. 5^7, February, 1927. 

11. Gibson, K. S., and Haupt, G. W., "Standardization of Lovibond Red Glasses in Combination with 
Lovibond 35 Yellow," J . Research Nat. Bur. Standards, No. 13, 1934. Haupt, G. W., "Departures from Ad- 
ditivity Among Lovibond Red Glasses in Combination with Lovibond 35 Yellow," Oil & Soap, November, 
1938. 

12. Colorimelry, The Tintometer, Ltd., Milford, Salisbury, England, 1939. 

13. Amy, H. V., and Ring, C. H., "International Standards for Colored Fluids and a Suggested Plan for 
Such Standardization," Proc Sth Intern. Congr. Applied Chemistry , 1912. Ring, C. IL, "Standardized Colored 
Fluids," J . Franklin Inst., August, 1915. Amy, H. V., "Color Standards and Colorimetric Assays," J. Ind. 
and Eng. Chem., April, 1916. 

14. Cooper, F. G., Munsell Manual of Color, Munsell Color Company, Baltimore, Maryland, 1929. Glenn, 
J. J., and Killian, J. T., "Trichromatic Analysis of the 'Munsell Book of Color,' " J. Optical Soc. Am., De- 
cember, 1940. Granville, W. C, Nickerson, D., and Foss, C. E., "Trichromatic Specifications for Inter- 
mediate and Special Colors of the Munsell System," J. Optical Soc. Am., July, 1943. Kelly, K. L., Gibson, 
K. S., and Nickerson, D., "Tristimulus Specification of the 'Munsell Book of Color' from Spectrophotometric 
Measurements," J. Optical Soc. Am., July, 1943. Munsell, A. H., A Color Notation, Munsell Color Company, 
Baltimore, Maryland, 1941. Munsell Book of Color, Munsell Color Company, Baltimore, Maryland, 1929. 
Munsell, A. H., Atlas of the Munsell Color System, Wadsworth Howland, Boston, 1915. See also: 

Munsell, A. E. O., Sloan, L. L., and Godlove, I. H., "Neutral Value Scales. I. Munsell Neutral Value 
Scale," J. Optical Soc Am., November, 1933. Newhall, S. M., Nickerson, D., and Judd, D. B., "Final Report 
of the Optical Soc. Am., Subcommittee on the Spacing of the Munsell Colors," J. Optical Soc. Am., July, 1943. 
Nickerson, D., "Spacing of the Munsell Colors," Ilium. Eng., June, 1945. 

15. Ostwald, W., Colour Science: Part I, Colour Theory and Standards of Colour: Part 1 1, Colour Measurement 
and Colour Harmony, Winsor & Newton, London, 1933. Taylor, J. S., The Ostvxild Colour Album, A Complete 
Collection of Colour Standards for Use in Colour Specifications and the Study of Colour Harmony, Winsor & New- 
ton, London, 1935. Jacobson, E., The Color Harmony Manual, Container Corporation of America, Chicago, 
Illinois, 1942. Foss. C. E., Nickerson, D., and Granville, W. C, "Analysis of the Ostwald Color System," 
J .Optical Soc. Am., July, 1944. 

16. Commission Internationale de l'Eclairage, Proc of the Eighth Session, Cambridge, England, September, 
1931. Commission Internationale de l'Eclairage Proc. of the Ninth Session, Berlin, Germany, July, 1935. 
Colorimetry Committee of the Optical Soc. Am., "Colorimeters and Color Standards," /. Optical Soc. Am., 
January, 1945. Judd, D. B., "The 1931 I.C.I. Standard Observer and Coordinate System for Colorimetry," 
J. Optical Soc. Am., October, 1933. Smith, T., and Guild, J., "The CLE. Colorimetric Standards and 
Their Use," Trans. 0. S. (Brit.), 1931-32. 

17. Judd, D. B., "The Computation of Colorimetric Purity," J. Optical Soc Am., and Rev. Sci. Instruments, 
February, 1926. Judd, D. B., "Reduction of Data on Mixture of Color Stimuli," J. Research Nat. Bur. 
Standards, April, 1930. Judd, D. B., "A General Formula for the Computation of Colorimetric Purity," 
J. Research Nat. Bur. Standards, May, 1931; J. Optical Soc. Am., November, 1931. Priest, I. G., "Apparatus 
for the Determination of Color in Terms of Dominant Wavelength, Purity, and Brightness," J. Optical Soc. 
Am., and Rev. Sci. Instruments, I. November, 1924; II. February, 1926. Priest, I. G., and Brickwedde, F. G., 
"The Minimum Perceptible Colorimetric Purity as a Function of Dominant Wavelength with Sunlight as 
Neutral Standard," J . Optical Soc. Am., and Rev. Sci. Instruments, August, 1927. 

18. Judd, D.B., "Estimation of Chromaticity Differences and Nearest Color Temperature on the Standard 
1931 I.C.I. Colorimetric Coordinate System," J. Research Nat. Bur. Standards, November, 1936; J. Optical 
Soc Am., November, 1935. Judd, D. B., "Sensibility to Color Temperature Change as a Function of Temp- 
erature," J. Optical Soc. Am., January, 1933. 

19. Ames, A., Jr., "Systems of Color Standards," J. Optical Soc. Am., and Rev. Sci. Instruments, March, 
1921. Judd, D. B., "Color Systems and Their Inter- Relations," Ilium. Eng., March, 1941. Moon, P., "Color 
Determination," Ilium. Eng., March, 1941. Nickerson, D., "Color Measurement, A Handbook of Disk 
Colorimetry," Misc. Pub. 580, U. S. Department of Agriculture, 1946. 

20. Nickerson, D., "Spacing of the Munsell Colors," Ilium. Eng., June, 1945. Newhall, S. M., Nickerson, 
D., and Judd, D. B., "Final Report of the Optical Soc. Am., Subcommittee on the Spacing of the Munsell 
Colors," J. Optical Soc. Am., July, 1943. 

21. Hardy, A. C, Handbook of Colorimetry, Technology Press, Cambridge, 1936. 



4-30 



I E S LIGHTING HANDBOOK 



22. Aristotle, "De Coloribus," Works of Aristotle, Vol. 6, Clarendon Press, Oxford, 1913. Birren.F., The 
Story of Color, The Crimson Press, Westport, Connecticut, 1941. Burris-Meyer, Elizabeth, Historical Color 
Guide, William Helburn, New York, 193S. Burris-Meyer, Elizabeth, This is Fashion, Harper & Brothers, New 
York, 1943. Burris-Meyer, Elizabeth, Color and Design in the Decorative Arts, Prentioe-Hall, Inc., New York, 
1935. Birren, F., Functional Color, The Crimson Press, New York, 1937. Cleland, T. M., A Practical Descrip- 
tion of the Munsell Color System, Munsell Color Company, Baltimore, Maryland, 1921. Chase, H. C, An Artist 
Talks About Color, J. Wiley & Sons, Inc., New York, 1930. Cutler, C. C, and Pepper, S. C, Modern Color, 
Harvard University Press, Cambridge, 1923. Graves, M., The Art of Color and Design, McGraw-Hill Book 
Company, Inc., New York and London, 1941. Hiler, Hilaire, Color Harmony and Pigments, Favor, Ruhl & 
Company, Chicago and New York, 1942. Jacobson, E., The Color Harmony Manual, Vols. 1-13, Container 
Corporation of America, 1942. Jacobs, Michael, The Art of Colour, Doubleday, Page & Company, New 
York, 1931. Luckiesh, M., Color and Colors, D. Van Nostrand Company, New York, 1938. Luckiesh, M., 
The Language of Color, Dodd, Mead & Company, New York, 1920. Luckiesh, M., Light and Color in Adver- 
tising and Merchandising, D. Van Nostrand Company, New York, 1923. Luckiesh, M., Color and Its Appli- 
cation, D. Van Nostrand Company, New York, 1921. Mayer, R., The Artist's Handbook of Materials and 
Technique, Viking Press, New York, 1940. Moon, P., and Spencer, D. E., "Geometric Formulation of Classi- 
cal Color Harmony," J . Optical Soc. Am., January, 1944. Ostwald, W., Colour Sciences: Part I, Colour Theory 
and Standards of Colour, Part II, Colour Measurement and Colour Harmony, Winsor & Newton, London, 1933. 
Pope, A., The Printer's Modes of Expression, Harvard Finiversity Press, Cambridge, 1931. Sargent, W., The 
Enjoyment and Use of Color, Charles Scribner's Sons, New York, 1923. Snow, B. E., and Froehlick, H. B., 
The Theory and Practice of Color, American Crayon Company, Sandusky, Ohio. 

23. Jacobson, E. G., "The Science of Color, A Summary of the Ostwald Theory," More Business, 1937. 
Jacobson, E., The Color Harmony Manual, Vols. 1-12, Container Corporation of America, Chicago, 1942. See 
also 22. 

24. Moon, P., and Spencer, D. E., "Area in Color Harmony," J . Optical Soc. Am., February, 1944. Moon, 
P., and Spencer, D. E., "Aesthetic Measure Applied to Color Harmony," J. Optical Soc. Am., April, 1944. 

25. Houghten, F. C, Olson, H. T., and Suciu, J., Jr., "Sensation of Warmth as Affected by the Color of the 
Environment," Ilium. Eng., December, 1940. 

26. Granville, W. C, "Color Control of Surface Coatings with Master and Working Standards of Color," 
Ilium. Eng., December, 1944. 

27. Nickerson, D., "Color Measurement, A Handbook of Disk Colorimetry," Misc. Pub. 580, U. S. De- 
partment of Agriculture, 1946. 

28. Judd, D. B., "Specification of Color Tolerances at the National Bureau of Standards," Am. J. Psychol. 
July, 1939. Judd, D. B., "Specification of Uniform Color Tolerances for Textiles," Textile Research, May and 
June, 1939. A Symposium on Color Tolerance, published by Inter-Society Color Council, P. O. Box 155, 
Benjamin Franklin Station, Washington, D.C. See also: 

Dimmick, F. L., and Hubbard, M. R., "The Spectral Components of Psychologically Unique Red." 
Am. J. Psychol., July, 1939. Dimmick, F. L., and Hubbard, M. R., "The Spectral Location of Psychologically 
Unique Yellow, Green, and Blue," Am. J. Psychol., April, 1939. Haupt, G. W., "Departures from Additivity 
Among Lovibond Red Glasses in Combination with Lovibond 35 Yellow," Oil and Soap, November, 1938. 
Judd, D. B., "Sensibility to Color Temperature Change as a Function of Temperature," J. Optical Soc. Am., 
January, 1933. Judd, D. B., "Estimation of Chromaticity Differences and Nearest Color Temperature on the 
Standard 1931 I.C.I. Colorimetric Coordinate System," J. Research Nat. Bur. Standards, November, 1936; 
J . Optical Soc. Am., November, 1936. Tyndall, E. P. T., "Chrornaticity Sensibility to Wavelength Difference 
as a Function of Purity," J. Optical Soc. Am., January, 1933. 

29. Judd, D. B., "Chromaticity Sensibility to Stimulus Differences," J. Optical Soc. Am., February, 
1932. Judd, D. B., "Sensibility to Color Temperature Change as a Function of Temperature, J. Optical Soc. 
Am. .January, 1933. Macbeth, N., "Color Temperature Classification of Natural and Artificial Illuminants," 
Trans. Ilium. Eng., Soc, March, 1928. Macbeth, N., "The Establishment of Proper Daylite Illuminants 
for Color Matching," Ilium. Eng., May, 1944. Nickerson, D., Computational Tables for Usein Studies of Arti- 
ficial Daylight, Agricultural Marketing Service, U. S. Department of Agriculture, August, 1940. Nickerson, 
D., "The Illuminant in Color Matching and Discrimination," Ilium. Eng., March, 1941. Priest, I. G., and 
Judd, D. G., "Sensibility to Wavelength Differences and the Precision of Measurement of Dominant Wave- 
length for Yellow Colors of High Saturation," J. Optical Soc. Am., and Rev. Sci. Instr., September, 1927. 
Priest, I. G., and Brickwedde, F. G., "The Minimum Perceptible Colorimetric Purity as a Function of Domi- 
nant Wavelength with Sunlight as Neutral Standard," J. Optical Soc. Am., May, 1938. Taylor, A. H., "In- 
fluence of Fluorescent Lighting on the Colors of Decorations and Furnishings," Ilium. Eng., July. 
1940. Taylor, A. H., and Kerr, G. P., "The Distribution of Energy in the Visible Spectrum of Daylight,' 
J . Optical Soc. Am., January , 1941. Tyndall, E. P. T., "Chromaticity Sensibility to Wavelength Difference 
as a Function of Purity," J . Optical Soc. Am., January, 1933. Wright, W. D., "The Measurement and Analysis 
of Colour Adaptation Phenomena," Proc. Roy. Soc, B-115, London 1934,. Wright, W. D., "The Breakdown of 
a Colour Match with High Intensities of Adaptation," J. Physiol., June, 1936. Weitz, C. E., and Cissell, R. F., 
"Spectral Analysis of Radiant Energy," Trans. Ilium. Eng. Soc, May, 1939. 

30. Nickerson, D., "Artificial Daylighting Studies," Trans. Ilium. Eng. Soc, December, 1939. Nickerson, 
D., "The Illuminant in Color Matching and Discrimination," Ilium. Eng., March, 1941. 

31. Visual Studies Sub-committee on Problem 13, "Preferred Illuminant for Color Matching," the Inter- 
Society Color Council. 

32. Gibson, K. S., "The Analysis and Specification of Color," J . Soc. Motion Picture Engrs., April, 1937 

33. Barnes, H. F., "Color Characteristics of Artists' Pigments," J . Optical Soc Am., May, 1939. 
Bustenoby, J. H., How to Mix Colors, J. S. Ogilvie Publishing Company, New York, 1935. 

34. Hardy, A. C, "A New Recording Spectrophotometer," J . Optical Soc. Am., September, 1935. 

35. Beckman, A. H., and Cary, C. H., "A Quartz Photoelectric Spectrophotometer," J. Optical Soc Am., 
November, 1941. 

36. Brode, W. R., and Jones, C. H., "Recording Spectrophotometer and Spectropolarimeter," J. Optical 
Soc Am., December, 1941. 

37. Colorimetry Committee of the O.S.A., "Colorimeters and Color Standards," J. Optical Soc Am., 
January, 1945. 

38. Barnes, B. T., "A Four-Filter Photoelectric Colorimeter," J. Optical Soc Am., October, 1939. 

39. Hunter, R. S., "A Multipurpose Photoelectric Reflectometer," J. Research Nat. Bur. Standards, No- 
vember, 1940; also J. Optical Soc. Am., November, 1940. Hunter, R. S., "Photoelectric Tristimulus Color- 
metry with Thru Filters," National Bureau of Standards Circular C-429, U. S. Department of Commerce 
1942. 



SECTION 5 
THE MEASUREMENT OF LIGHT 

The fact is well established that progress in a branch of science or en- 
gineering is expedited materially by each advance in measuring technique 
and by each improvement in measuring apparatus. 

The measurement of light is called photometry and devices used for this 
purpose are usually called photometers. 

For many years photometric measurements dependec. on visual observa- 
tions. The characteristics of the human eye vary widely in groups of 
observers, and over a period of time even in one observer in an unpredict- 
able manner. Because of these variations the accuracy and precision 
practically attainable with visual photometers is limited. 

Although physical photometers, utilizing photoelectric cells, thermo- 
piles, or bolometers, are not subject to the errors introduced by the vari- 
able characteristics of the human eye, frequent calibration is necessary if 
the maximum practicable accuracy and precision of which they are capable 
is desired. 

The response characteristics of many photosensitive elements vary be- 
tween individual samples of the same type and manufacture, are not con- 
stant with time, and, except when compensated (with a special filter, for 
example), are not similar in spectral response characteristics to the stand- 
ard (I.C.I.) observer. (See Fig. 1-2, page 1-5.) When the spectral 
distribution (color) of the light measured is not the same in every case as 
the standard used in calibrating the instrument (the colors of natural 
daylight, incandescent, fluorescent, mercury and sodium lamps are differ- 
ent) this deviation from I.C.I, response characteristics may introduce 
very large errors. The most common types of light meters which employ 
barrier -laj^er cells are also subject to errors introduced by a variation in 
the angle of incidence of the light being measured. Thus it is evident 
that the measurement of light is a painstaking task requiring skill, care, 
and common sense as well as good equipment. 

Measurable Characteristics 

. As indicated in Table 5-1, many characteristics of light, light sources, 
lighting materials, and lighting installations may be measured. The 
measurements of most general interest are: 

1. Illumination. 

2. Brightness. 

3. Intensity in a specific direction, and intensity distribution. 

4. Luminous flux. 

5. Color temperature. 

6. Spectral distribution. 

Basic Photometric Principles 

Almost every photometric measurement involves a consideration of the 

Note: References are listed at the end of each section. , 

1 



5-2 



I E S LIGHTING HANDBOOK 



Table 5-1. Some Measurable Characteristics of Light, Light Sources, 
and Lighting Materials 



CHARACTERISTIC 



DIMENSIONAL UNIT 



EQUIPMENT 



TECHNIQUE 



LIGHT 



Wavelength 


micron 


Interference 
grating 


Laboratory 


Color temperature 


degree 


Pyrometer 


Laboratory 


Flux density 


lumens/sq ft 


Photometer 


Laboratory or field 


Orientation of po- 


degree (angle) 


Analyzing Nicol 


Laboratory 


larization 




prism 




Degree of polariza- 


per cent 


Polarization pho- 


Laboratory 


tion 




tometer 







LIGHT SOURCES 






Energy radiated 


ergs/s.q in. 


Calibrated radi- 
ometer 


Laboratory 




Luminous intensity 


candle 


Photometer 


Laboratory or 


field 


Brightness 


footlambert 


Photometer or 
brightness meter 


Laboratory or 


field 


Spectral energy dis- 


ergs/micron 


Spectrometer 


Laboratory 




tribution 










Power consumption 


watt 


Wattmeter, or (for 
dc and 100 per 
cent power fac- 
tor a-c circuit) 
voltmeter and 
ammeter 


Laboratory or 


field 


Light output (total 


lumen 


Integrating sphere 


Laboratory 




flux) 




photometer 









LIGHTING MATERIALS 






Reflectance 


per cent (dimen- 
sionless ratio) 


Reflectometer 


Laboratory or 


field 


Transmittance 


per cent (dimen- 
sionless ratio) 


Photometer 


Laboratory or 


field 


Spectral reflectance 


per cent (at spe- 


Spectrophotometer 


Laboratory 




and transmittance 


cific wave- 
lengths) 








Optical density 


dimensionless 
number 


Densitometer 


Laboratory 





inverse-square law (which is strictly applicable only for point sources) 
and the cosine law. 

The inverse-square law (see Fig. 5-1) states that the illumination E 
of a surface varies directly with the candlepower i" of the source and in- 
versely as the square of the perpendicular distance d between the source 
and the surface : 

E = i 

d 2 

This holds true only when the maximum dimension of the source (or 
luminaire) as viewed from the surface, is small (subtending less than 



THE MEASUREMENT OF LIGHT 



5-3 



illumination: 



POINT SOURCE 
(|NTENSITY = I) ___--" 



F --i- c — I- 
'- d 2 E 2.- 4 d2 



d 2 t 2 d2 u Z 4d j 



•COS 9 




FIG. 5-1. The inverse -square law describes the geo- 
metrical relationship between a source and a surface 
illuminated by light from that source. Surfaces A and 
AAAA are portions of spheres with centers at the light 
source. 



one fifth the distance between source and surface) and when the surface 
approximates a portion of a sphere of radius d with its center at the source. 
The cosine law states that the illumination of any surface varies as the 
cosine of the angle of incidence 6 (between the normal to the surface and 
the direction of the incident light) : 

E = 4 cos 6 
d- 

The cosine-cubed law or combined law is a convenient derivation which 
is useful in many situations encountered in practice. The illumination 
of any element of surface is equal to the sum of the individual components of 
illumination produced by each contributing source. The individual com- 
ponents of illumination E 6 vary as the intensity Ig of the source in the 
direction of the element and the cube of the cosine of the angle of incidence 
0, and inversely as the square of the perpendicular distance h of the source 
above the element. For a number of point sources of which the location 
and candlepower in the direction of the element are known, this law may 
be expressed : 

E = 2 Ig cos 3 0/A 2 

Values of the trigonometric functions may be obtained from Appendix 
Table A-25, page A-39. For surface sources the function must be integrated 
for values of d included between the bounding angles of the source. (See 
page 8-46.) 

• Comparison with a standard source. In theory, each photometric meas- 
urement is made by direct visual comparison with light sources which 
have been established by international agreement as standards of candle- 
power. (See page 3-2.) In practice, however, the comparison is in- 
direct. The laboratory reference standard lamp is used instead of one 
or more basic standards such as the national standard carbon lamps. 
(See figure 3-1.) Since an observer cannot measure or judge visually 
with any degree of accuracy the intensity or lumen output of a source, 



5-4 I E S LIGHTING HANDBOOK 

or the illumination or brightness of a surface, but can detect a very small 
difference in brightness between two surfaces, visual photometers usually 
provide for the convenient and simultaneous visual comparison of two 
immediately adjacent fields, one illuminated by the test source and one 
by a laboratory source of which the characteristics are known. By vari- 
ous means, the brightness of one or both fields may be adjusted until the 
two appear equally bright. The intensity of the test source may then 
be determined by means of the instrument calibration or by application 
of the inverse-square and cosine laws. 

Physical photometers of which the spectral response approximates that 
of the I.C.I, observer eliminate the necessity for visual observation. 

Field Measurements 

It is often desirable and necessary to make photometric measurements 
outside 'the laboratory, and portable instruments have been developed 
for this purpose. Typical problems include interior and exterior lighting 
surveys of which a common objective is the compilation of reliable data on 
a new T installation sufficient to determine compliance with specifications or 
recommended practice. Analysis of such data on an old installation may 
reveal the need for maintenance, modification, or replacement. 

Since the method used may exert a great influence on the results of 
photometric measurements (particularly of those made in the field) the 
necessity of adhering to standardized procedures of measurement and in- 
terpretation is generally recognized. Such procedures have been de- 
veloped by the Illuminating Engineering Society for obtaining the illu- 
mination in typical interior areas and the general principles set forth in 
these may be applied to the solution of other field survey problems. How- 
ever, for equivalent accuracy, larger numbers of readings will probably be 
required in other cases since the procedures outlined on page 5-6 are 
the only standardized, short-cut, field methods available and were de- 
veloped for specific application only under the described conditions. 

The National Electrical Manufacturer's Association has developed a 
survey procedure for floodlighting installations which has been accepted 
by its members. A condensation is reproduced beginning on page 5-8. 

Isolux diagrams such as those shown in Figures 8-20 and 8-21 en page 
8-49 in most cases are obtained by taking readings at equally spaced in- 
tervals in representative areas, as, for example, along the straightaway, 
at intersections, and at curves. It has been proposed that street and 
highwaj^ fighting surveys may be made also through the analysis of care- 
fully prepared photographs. 1 

The probability of error when making footcandle measurements in the 
field is relatively high. Accuracies must not be expected that are beyond 
the limitations of the instruments used. Since illumination measurements 
apply only to the actual conditions existing during the survey (voltage, 
hours of burning, depreciation, and so forth), it is extremely important to 
record a detailed description of the illuminated area and existing condi- 
tions in the survey report. 



THE MEASUREMENT OF LIGHT 



5-5 



Interior Lighting Survey Procedure 

Light source seasoning period. No readings should be reported for dis- 
charge-source systems unless they have been operated for. a total of at 
least 100 hours. The fluorescent type; particularly, requires not less than 
100 hours of operation before stabilization of the light output can be ex- 
pected. The published average depreciation during this period is approxi- 
mately 10 per cent but field experience indicates that it may be higher 
in individual cases. With incandescent lamps, seasoning is accomplished 
by six hours operation at labeled volts. , 

Warm-up period. No readings should be taken of a discharge-source 
system until it has been in continuous operation at least half an horn*. 
The light output of discharge sources, particularly fluorescent lamps, 
varies with ambient temperature, decreasing appreciably from rated 
values if the temperature adjacent to the lamp rises above or falls below 
the design ambient. The upper limits are often exceeded in poorly ven- 
tilated luminaires and a decrease in light output during the first half hour 
of operation results. 

Standard record form. The official I.E.S. footcandle survey form, IS- 
10 (see Fig. 5-2), which may be ordered from stock at I.E.S. headquarters 
(51 Madison Avenue, New York 10, New York) should be used for re- 
cording survey data. Each form is accompanied by supplementary sheets 
rom which the following measurement procedures were condensed. 2 



FOOTCANDLE SURVEY FORM (IS-io) 
For Artificial Illumination in Interiors 



DateofSurvcy Time A.M.. P M. Appro*. Room Temperature in Area 

Insttument Used . Mfr , Name * Model 

Equipped svith color correciion filler □ ycj D no. Dale ol last calibraiion 

(Cell type instruments should be at a temperature above fo'F if possible and 
should have their tells exposed 10 the approximate illumination level 10 be meas- 
ured lor at least is minutes befoie taking readings.) 



and type ol 
Lengih 





C.,„ 


M.te.ia, 


«_ 


K fr" 


I, the Surface 


D *"' PL ™ 


Clean 


ltd," 


Decidedly 


Side Walls 










□ 


a 


D 


Ceiling 










□ 


a 


a 


Floor 










D 


a 


D 


Work Surfaces 










D 


D 


D 



Description of General Lighting System 

Date of completion of lighting installation Approx. hours" use since installation 

(If gaseous source, system must have been 

lighted for at least | hour before measurements arc taken 

Type of Light Source . to be lure that normal operating output has been 

attained. No gaseous source system should be meas- 
ured until at least too hours of operation have elapsed.) 

Number and wattage of lamps per lu rain lire . .. .. ., 

Rated Voltage oflamps Socket Voltage Color 



As Prepared by the 111 



ng Engineering Society 



Joveri 



Type of Luminaitc (IC1 Classification) 
Mfr. Name Cat. No. 

No. of Photometric Test .. Wattage per Luminairc 

(including auxiliaries) 
No. of Luminaires Spacing (If area is irregular show sketch) 

Mounting Mounting Height above flour oofoveri!l suspension 

Condition of Equipment G Freshly cleaned D Average D Dirty 

Description of Supplementary or Local Lighting 

Measurement Data 
Average Horizontal Footcandles IK Regular Areas From General Ligh- 

(Illumination at point of measurement net to be obstructed by operative or 

Plane [ Horizontal— jo" above floor ft-cl . 

Plane, (Describe) ft-c S " *"* 

Plane j (Describe) . .. . ft-c] inmU " 

Make Sketch and show values following general procedure outlined for rcg 
Footcandle l /.t Point of and in Plane op Work 



Descriplion ol Locaiion 


S" 


Hoc. Plane JVC. Plane 


nwgg 


Foolcand.e, 




















(Check 


Which) 


U Plus Local 


Only 


A- (Max) 




D 


n 


• 1 




B (Min) 




a 


n 








C 




a 


o 






















E 

F 




a 

D 


□ 

D 









FIG. 5-2. Standard I.E.S. interior lighting survey report form IS-10 (reduced). 



5-6 I E S LIGHTING HANDBOOK 

PROCEDURES FOR DETERMINING AVERAGE HORIZONTAL FOOTCANDLES IN 

REGULAR AREAS 

The flux of light method is employed to obtain the value of average foot- 
candles. This is the quotient of total lumens on the working plane (30 
inches above the floor) by the area in square feet. 

The use of these procedures in the types of areas described should re- 
sult in a value of average illumination within 10 per cent of the value that 
would be obtained by dividing the area into 2 foot squares, taking a read- 
ing in each square, and averaging. Except for the most exact specifica- 
tion, therefore, the saving in time to be made by using the suggested meth- 
ods would justify this 10 per cent error. 

Regular area with symmetrically spaced individual luminaires in two or more 
rows. (1) Select an inner bay of four units as shown in Fig. 5-3a. Take 
four readings (r, r, r, r). Repeat in a centrally-located bay and average 
the eight readings. (2) Select a half bay at each side of the room. Take 
two readings (q, q) in each midway between line of outside units and the 
wall, and average the four readings. (3) Select a half bay at each end 
of the room. Take two readings (t, t) in each midway between line of 
end units and the wall, and average the four readings. (4) In one corner 
of the room take one reading (p) as shown. Repeat in another corner and 
average the two readings. 

. .„ . .. AX(B-1)X(C-1) + DX(B-1) + EX(C-1)+F 

Average illumination = - : — : ■ 

number of luminaires 

where A = ft-c (step 1) 

B = number of luminaires per row 

C = number of rows 

D = ft-c (step 2) 

E = ft-c (step 3) 

F = ft-c (step 4) 

Regular area with single row of individual luminaires. (1) Select two 
half bays on each side of the room and take two readings (q, q) in each, 
as in step 2 above. Average the eight readings. (2) In one corner of 
the room take one reading (p), as in step 4 above. Repeat in another 
corner and average the two readings. 

Average illumination = 

(ft-c, step 1) X (number of luminaires minus 1) (ft-c, step 2) 
number of luminaires 

Regular area with single luminaire. (1) In each quadrant of the room 
take one reading (p), as in step 4 above. Average the four readings: 

.„ . . 2ft-c 
average illumination = 

Regidar area with two or more continuous rows of luminaires. (1) Take 
four readings (r, r, r, r) near center of room as shown in Fig. 5-36 and 
average the four readings. (2) At each midside of room take one reading 
(q) midway between the outside row of units and the wall as shown. 



THE MEASUREMENT OF LIGHT 



5-7 



w 


o 


o 


£ 9 -^ q 


o 


o 


o 




o 
o 


o 

o 


Q-S--9 


o 
o 


o 
o 


o 

o 


O 


o 


o 


o o 


o 


o 


o 


O 





o 


o o 


o 


o 


o 


O 


o 


o 


o o 


o 


o 


o 


O 


o 


o 


o o 


o 


o 


o 


o 


o 


o 


o o 





o 


o 



**'P ,q» 






tj ! 1 * r i 1 * r 1 I , 


,\*i » r ,r 

' 1 II 1 1 1 ' 




1 1 1 1 1 ' 1 


1 1 1 1 1 1 1 1 





\ A - 

\p/ 1 

* 


q» 


q. 


q* 


"■ 





FIG. 5-3o. Location of illumination measurement stations in regular area with 
symmetrically spaced individual luminaires in two or more rows. b. Location of 
illumination measurement stations in regular area with two or more continuous 
rows of luminaires. c. Location of illumination measurement stations in regular 
area with one continuous row of luminaires. 



Average the two readings. (3) At each end of room take two readings 
(t , t) one at end of a row midway between end of row and the wall, the other 
between rows and midway to wall as shown. Average the four readings. 
(4) In one corner take one reading (p) as shown. Repeat in another 
corner and average the two readings. 

AXBX(C-1)+DXB + EX(C-1)+F 



Average illumination = 
where 



X 



B 



C 

A = ft-c (step 1) 

B = number of luminaires per row 

C = number of rows 

D = ft-c (step 2) 

E = ft-c (step 3) 

F = ft-c (step 4) 

Regular area with one continuous row of luminaires. (1) Divide the con- 
tinuous row into four equal lengths. Opposite each of the three division 
points and midway between the row of units and the wall, take a read- 
ing (q). Repeat on the opposite side and average the six readings. (2) 
In one corner take one reading (p) as shown in Fig. 5-3c. Repeat in another 
corner and average the two readings. 

Average illumination = 

(ft-c in step 1) X (number of luminaires per row) + (ft-c in step 2) 
number of luminaires plus 1 



5-8 I E S LIGHTING HANDBOOK 

Floodlighting Survey Procedure for Baseball and Football Field Installa- 
tions. 

In-many floodlight installations light is projected in a direction forming 
a large angle of incidence with the surface to be lighted, and each unit 
must be, adjusted carefully to produce the best utilization. This also 
necessitates the application of special care in the measurement of the 
resultant illumination. The, following is a condensation of the recom- 
mended practice developed by the National Electrical Manufacturer's 
Association. 3 f ; 

Preparation for the survey. (1) Inspect and record the condition of the 
reflectors. (2) Record the mounting height of the floodlights. (3) 
Record ; the location of the poles and the number of units per pole ; the 
wattage of the lamp ; and the direction of aim. Check these data against 
the recommended layout ; a small change in the location or adjustment of 
the floodlights may make a considerable difference in the resultant illu- 
mination. (4) Determine and record the hours of burning of the in- 
stalled lamps. The test should be made with seasoned new lamps. (5) 
Record the atmospheric conditions. Because of the effect of smoke, fog, 
and so forth, survey should be made only when atmosphere is clear. (6) 
Record the voltage at the lamp socket with all lamps operating, at night 
during the hours when the floodlights will normally be used. A check of 
the voltage at the main switch or during the daytime is valueless. The 
light output of large incandescent lamps varies approximately 3.5 per cent 
with every 1 per cent change in voltage. If the measured voltage is not 
exactly the rated voltage of the lamp, this correction should be applied 
to the footcandle readings obtained before comparing them with calcu- 
lated values. 

Survey procedures. Measurements should be made by an experienced 
operator with a properly calibrated Macbeth illuminometer "(Fig. 5-7 a) 
or other photometer corrected for angle of incidence error. It is par- 
ticularly important to see that the test plate is absolutely level whatever 
meter is used.* Level the test plate before taking measurements at each 
station. 

1. Place the test plate on a firm support 24 inches above the ground 
and take readings at each of the test stations shown in Fig. 5-4. 

Stations for the baseball field are on 45-foot centers on the infield and 
on 60-foot centers on the outfield. Stations for the football field are 
located on lines parallel to the goal line, spaced 10 yards apart. Measure- 
ments should be made at seven stations equally spaced in each line across 
the field. It is necessary to take readings on only one half the field. 

2. At each station average three separate readings and avoid casting 
shadows on the plate during the reading. 



* Because of the large angle of incidence at which light from a floodlighting installation usually strikes a 
horizontal playing field, large errors are introduced into measurements made with common types of illu- 
mination meters employing barrier-layer cells. Correction for this error must be made if such a meter is used 
for taking readings. The correction procedure is outlined on page 5-12. The design of the General Electric 
multicell color corrected diffusing plate is such that the incidence error is minimized. (See Fig. 5-5.) 



THE MEASUREMENT OF LIGHT 



5-9 



JT' 

i 
i < 

!' 

120 
FT 1 

i J-i 

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60 FT 

f" 

60'fT 

I ' 



->4* 60 FT *1*60 FT*+* 60 FT*-| 

-© ©-. 



GOAL LINE 
t 

© — e — © — ©- 



e ^ 



50-YD LINE 

■^ 

1 

' SEVEN , 

STATIONS 
©■ ^-(-—EQUALLY 



GOAL LINE 

L 



© O 



-© ©— © © 



-J 
I 



FOOTBALL 



LOCATION OF 
TEST STATIONS 



BASEBALL 



FIG. 5-4. Location of illumination measurement stations on football and baseball 

playing fields. 

3. Check the milliammeter reading on the illuminometer frequently to 
ensure proper calibration. More consistent readings are obtained at the 
expense of frequent battery replacements if the comparison lamp is on 
throughout the test. 

4. When readings have been completed recheck those at the first station. 

Calculated footcandles. The calculated footcandles for a given installa- 
tion are based upon the results of photometric tests of individual units 
which are accurate within plus or minus 2 per cent for the ideal conditions 
of the photometric laboratory. These results apply to an absolutely clean 
average reflector and are made under controlled conditions with new lamps 
selected and standardized for their rated lumen output. The lamps are 
operated at exactly the correct voltage to produce the rated lumen out- 
put. Despite proper application of Utilization and depreciation factors in 
the computation, it is' not possible to predict the resultant illumination 
produced in the actual installation with equal accuracy in every case 
because of uncontrollable variables encountered in the field. 

A number of more or less portable photometric devices have been de- 
veloped for use in the field. These must be expected to suffer the ills to 
which most portable devices are susceptible and therefore for reliable re- 
sults must be transported and used carefully, and calibrated frequently. 

Portable photoelectric photometers 

The convenience and portability of photoelectric devices such as shown 
in Fig. 5-5 have given them preference over the visual illuminometers for 
lighting survey work. However, devices which utilize photoelectric cells 
are very likely to vary in sensitivity and may not have spectral response 
characteristics similar to those of the human eye. These and other char- 
acteristics are the cause of a number of errors. 4 - 5 

Spectral sensitivity curve. Representative characteristics of several dif- 



5-10 



I E S LIGHTING HANDBOOK 




FIG. 5-5. Portable photoelectric illumination meters (selenium barrier-layer cell): 
(a) Weston; (6) General Electric; (c) Westinghouse. 

ferent cells are shown in Fig. 5-6a. In 1937 the I.E.S. Committee on 
Photoelectric Portable Photometers recommended that barrier -layer cell 
photometers be calibrated by the use of unmodified radiation from an in- 
candescent lamp source operating at a color temperature of 2,700K. 5 
To correct the readings obtained with sources of other spectral characteris- 
tics, multiplying factors usually available from the manufacturer are used. 
Figure 5-66 shows the variation of multiplying factor with color tempera- 
ture of calibration source and test source calculated for uncorrected cells 
of representative spectral characteristics. 5 For light sources commonly 
used in interiors, this error may vary from 5 per cent to 25 per cent. 

Some cell-type instruments are equipped with filters which give the 
cell the approximate response of the eye and this error is thus minimized. 
When thus corrected, the meters evaluate sources with fairly uniform spec- 
tral emission well enough for most illuminating engineering purposes. 6 - 7 - 8 - 9 



THE MEASUREMENT OF LIGHT 



5-11 











/ 


\ 














COPPER 


/ 


\ 














OXIDE 


h 


A 




















H 




















^ v 












; 




, \ 
















\ \ 










SELENIUM^/" 






\ \ 










*•* 








\ > 






























,+* 










v 


\ 






*■''' 










s. 









0.5 0.6 0.7 

WAVELENGTH IN MICRONS 



1.2 
I.I 

o 

i i.o 

U- 

U 

Z 0.9 

0. 


















b 








SELENIUM 










/ 
/ 




v I 

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COPPER"" 
OXIDE 


s 


^ 


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2 0.7 
0.6 


















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^60 





THERMO-/.. \ 
PILE' 1 !' \\ 






c 








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V 


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ll 
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ij 




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1, 
il 






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W-CELL 












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2,000 3,000 4,000 6,000 10,000 20,000 

TEMPERATURE OF BLACKBODY RADIATION 
IN DEGREES KELVIN 




0.40 



0.76 



0.45 0.50 0.55 0.60 0.65 0.70 

WAVELENGTH IN MICRONS 

1 micron = 10,000 angstroms = 1/10,000 centimeters 



FIG. 5-6a. Relative spectral sensitivity characteristics of typical copper oxide 
and selenium barrier-layer cells, b. Multiplying (correction) factor versus color 
temperature for uncorrected cells of representative spectral characteristics. 6 c. 
Spectral transmittance curves for filters designed to correct, the spectral sensitivity 
characteristic of barrier-layer cells and thermopiles to correspond with I.C.I, ob- 
server. "Viscor" and "Barnes" filters are designed for use with selenium cells. 

Methods of measuring ultraviolet energy have been described also. 11 
Adaptation level. Like the human eye, many photocells increase in 
sensitivity when kept in the dark for periods extending over several hours. 
A normal reading can be obtained only after the cell has been adapted by 
exposure to the light for a period which for different instruments of the 
same type may vary between several minutes and several hours. The 
way to determine the interval for a particular instrument is to observe 
over a period of time the output (meter reading) of a dark-adapted cell 
(12 hours in the dark) when it is exposed to a constant illumination. 
Adaptation is complete when the readings remain constant. The cell 
must be exposed to each new level of illumination (variation of ±10 
footcandles) for this period before accurate readings may be obtained. 
The error due to lack of adaptation will not exceed about 5 per cent and 
therefore may usually be ignored in field work. 

Angle of incidence {cosine law). Light which strikes the face of a cell 
is reflected from the cover glass and the cell surface, and may be obstructed 
by the rim of the case. The magnitude of these effects varies with the 
angle of incidence, and an error of the order of 25 per cent can be expected 



5-12 I E S LIGHTING HANDBOOK 

when measuring illumination in large areas where the luminaire has a 
widespread light distribution and in any area where light walls, floors, 
and ceilings contribute an appreciable amount of flux. Multicell meters 
such as that shown in Fig. 5-5 are so constructed that the cosine error is 
nearly eliminated. 8 The Macbeth illuminometer may also be used to 
avoid this error. 

Correction for cosine error. The component of illumination contributed 
by sources at large angles of incidence may be determined by orienting the 
target perpendicular to the directions from which the light is coming and 
multiplying the readings thus obtained by the cosines of the angles of inci- 
dence. 

A method for correcting this cosine error by means of a special scale and 
shadow caster which permits the use of the cell in its normal horizontal 
position has been described and other means have been proposed. 5 ' 10 

Temperature effect. Temperature affects cell output, but not in a con- 
stant or predictable manner. To be on the safe side, the instrument 
should be calibrated at the air temperature of the space being investigated, 
preferably within the range of 60 degrees to 90 degrees Fahrenheit. Pro- 
longed exposure to temperatures above 120 degrees Fahrenheit will per- 
manently damage selenium cells. Hence measurements of high levels 
should be made rapidly to avoid overheating of the cell. 

Accuracy of meter readings. The microammeter used in connection 
with photoelectric instruments, in common with other electrical instru- 
ments, is subject to certain inherent limitations in the form of scale errors 
which vary in amount with the quality of the instrument. If the instru- 
ment has more than one scale, these should be so employed that no read- 
ing is taken in the range from zero to one fourth of full scale. Neglecting 
the factors noted above, the manufacturing tolerances alone may result 
in an over-all uncertainty of reading at any point on* the scale of about 
±7.5 per cent of the full scale reading. 

Calihration. Cell-type instruments have no provision for field cali- 
bration other than a zero reading correction. They should be checked 
frequently against a master instrument of known calibration or returned 
to a reliable laboratory at frequent intervals for calibration. 

Portable visual photometers * 

The portable photometer or illuminometer is a bar photometer on a 
small scale. There are a number of different types available but the under- 
lying principles are about the same. A fixed photometer head and moving 
comparison lamp is often used and some are combined with a photoelectric 
photometer. 

When using the portable photometer to measure illumination, it is 
customary to observe the brightness of a calibrated test plate. For 
brightness determinations, the field to be observed is seen directly through 
the eyepiece, and balanced with the comparison surface. This type of 
photometer is usually accompanied by a set of neutral and colored filters, 
which respectively extend the range and produce an approximate color 



THE MEASUREMENT OF LIGHT 



5-13 



match between the test and the comparison surfaces. The color filters 
usually should be placed between the comparison lamp and the comparison 
surface. 

The Macbeth illuminometcr, shown in Fig. 5-7a, consists of a Lummer- 
Brodhun cube, eyepiece, and comparison-lamp tube. Though less com- 
pact and more complex in its application than the photocell-type meters, 




PHOTOMETRIC 
FIELD 




ROTATE TO BALANCE 
PHOTOMETRIC SCALE 



BRIGHTNESS 
SCALE 



FIG. 5-7o. The Macbeth illuminometer. b. The Luckiesh-Taylor brightness 
meter. 



it is self contained in a carrying case and is a portable instrument. A 
diffusing-glass comparison surface (viewed by transmitted light) is illu- 
minated by a lamp in a diaphragmed enclosure which is moved in the 
comparison -lamp tube by a rack and pinion. The illuminometer may be 
equipped with a lens to bring into focus and restrict the test field. An 
inverse-square scale is marked upon the rod moving the comparison lamp. 
Provision is made for inserting neutral filters by which the range of the 
instrument is made to cover 0.001 footcandle to 10,000 or more foot- 
candles. A control box carrying rheostats and a meter on top, with a com- 
partment below for two No. 6 'dry cells, is regularly furnished along with a 
diffusing test surface and a reference standard for recalibration. The 
reference standard consists of a lamp in a housing having a hole for inser- 
tion of the sight-tube so that the test-surface may be viewed. The illu- 
mination incident upon the test-surface when a predetermined current is 
passed through the lamp is known and serves as the basis for calibrating 
or checking the readings of the illuminometer. Since the luminous re- 
flectance of the test-surface is known or determinable, for normal illumina- 
tion and observation in the 45- to 55-degree zone the reference standard 
also serves to calibrate the instrument for readings of brightness in foot- 
lamberts (the product of the illumination, i.e., footcandles, by the lumi- 
nous reflectance of the test-surface). 12 This instrument is capable of 
-measurements uncertain by only abcmt ±1 per cent when used by an 
experienced observer. 

The Luckiesh-Taylor brightness meter, shown in Fig. 5-76, is entirely 
self contained. The batteries fit into the case which has a control rheo- 
stat and scale on the side. The current is set for the calibration mark and 
maintained at that mark while measurements are being made. There is a 



5-14 



I E S LIGHTING HANDBOOK 



PROJECTOR 



MICROAMMETER 

m 



lens for focusing the light from the source and an eyepiece for viewing the 
photometric field. The optical system presents a split field Avith the test 
field in the center and the comparison fields on either side. The compari- 
son-field brightness is adjusted by turning a knob. When a photometric 
balance has been obtained, the reading is seen on an illuminated scale 
viewed through a magnifier located just below the eyepiece. Neutral 
filters extend the range. In the hands of an experienced observer photo- 
metric balances can be reproduced with a variation of 1 or 2 per cent ; 
scale and filter errors are usually somewhat larger. 13 

Miscellaneous field equipment 

Reflectometers. The Taylor reflectometer, and the General Electric 
light cell reflectometer shown in Fig. 5-8 are similar instruments. The 
former is designed for visual measurements (normally equipped with an 
opening for a Macbeth illuminometer) . The latter makes use of the bar- 
rier-layer cell as the measuring device. Both are small portable spheres 

with a surface opening for the test 
sample. A collimated beam is incident 
on the sample at about 45 degrees and 
the total reflected light is integrated 
by the sphere. The tube carrying 
the light source and the collimating 
lenses can be rotated so that light is 
incident directly on the sphere wall 
for the unreflected or 100 per cent 
reading. The sample is in place dur- 
ing both measurements and thus may 
be considered a part of the sphere 
so that the effect on both readings of 
the small area it occupies is the same. 
The ratio of the reading when light is 
incident on the sample, to the read- 
ing when the light is incident on the 
sphere wall is the luminous reflectance 
for the conditions of the test. The 
light cell reflectometer is designed to be 
used also with another sphere source giving diffuse illumination for meas- 
urement of luminous transmittance as shown in Fig. 5-8. The transmit- 
tance thus determined is the total transmittance for diffuse incident light. 14 
The Luckiesh-Moss visibility meter shown in Fig. 2-14 on page 2-16 is 
used to determine the visibility of an object or task. 

Laboratory measurements 

Because many of the variables encountered are uncontrollable and there- 
fore limit the accuracy and precision of field measurements, more reliable 
data may usually be obtained in the laboratory. Therefore whenever it 
is at all convenient photometric measurements should be made in a labo- 
ratory properly planned and equipped for this work. 




ILLUMINATOR- 



FIG. 5-8. The General Electric 
light cell reflectometer showing 
arrangement for transmittance 
measurements. 



THE MEASUREMENT OF LIGHT 5-15 

Most laboratories well equipped for general photometric work make use 
of the following basic types of equipment : 
Bar photometer. 
Integrating sphere. 
Distribution (gonio) photometer. 

In order that uniform results may be obtained by different laboratories, 
the Illuminating Engineering Society has developed standard procedures 
for several types of measurements: 

Diffuse enclosing-globe luminaires 15 . 

Semi-indirect enclosing-globe luminaires 16 . 

Direct luminaires 15 . 

Indirect luminaires 16 . 

Semi-indirect luminaires 15 . 

Narrow-beam enclosed projectors 16 . 

Incandescent filament floodlights 17 . 
Each of these procedures, which are combined here for handbook ex- 
planation, have been discussed in detail in the references indicated. While 
the handbook condensation is in agreement with the original in each case, 
it is recommended that the detailed reports be studied for additional 
guidance. 

General. The tests shall be conducted by a reliable laboratory « which 
certifies by its signature that the tests have been .conducted in accordance 
with the I.E.S. specifications tand that the data are accurate. A prominent 
note to the effect that the test results are typical only when all test con- 
ditions such as light center position and so forth are reproduced should be 
included. A standard illuminating engineering data form will be made 
available by the Society for reporting tests on general illumination 
luminaires. 

DATA TO BE REPORTED 

Manufacturer's name. 

Name or type of luminaire. 

Manufacturer's catalog numbers. 

Number of samples submitted (minimum of six). 

Lamps : 

Type. 

Number per luminaire. 

Watts each. 

Total watts including auxiliary control equipment. 

Volts, bulb size, base, service, filament construction, color, type of bulb glass. 

Light center. 

Rated lumens each. 

Power factor. 
Description of luminaire: 

I.E.S. classification. 

Applicable I.E.S. performance recommendations. 

Materials. 

Luminous reflectance and/or transmittance. 



5-16 I E S LIGHTING HANDBOOK 

Dimensions including husk and stem; may be given on dimensioned scale draw- 
ing. (See Fig. 5-9a.) 
Light center position during test. 

Distance from cap of lamp base to plane of fitter screw. 
Weight, also maximum and minimum weights of six samples tested. 

Method used for standardizing lamp and for calibrating photometer. 

Candlepower distribution, brightness, and light flux values as in Fig. 5-96. 

Total lumen output (in terms of bare lamp lumens). 

Testing distance. 

Description and explanation of any deviation from standard test conditions or 

procedure. 

Total efficiency. 

Permissible spacing ratios (relative to mounting height). (See page 8-22.) 

* Maximum beam candlepower as recorded in prescribed beam exploration. 

* Average maximum beam candlepower. 

* Beam spread in degrees in vertical and horizontal directions. 

* Outline of the beam. (See Fig. 14-4c.) 

* Tabulation of lumens for test area explored. 

* Beam efficiency. 

* Average lumen distribution in beam. 

* Beam lumens. 

* Average isocandle curves. 

Selection of luminaires for test. Six samples should be selected at ran- 
dom from stock and weighed. The lightest, the heaviest, and the three 
samples closest to average weight should be selected for the over-all 
light output test. The sample having the output closest to the average 
of the five should be used for all other tests and should be the unit to which 
the descriptive data reported apply. f 

Preparation for photometric tests. As many as possible of the variables 
which may introduce error into the results of the tests should be elimi- 
nated or minimized. Dust, grease, and so forth should be removed from 
all optical surfaces of lamp, luminaire, and apparatus. Stray light should 
be eliminated and all mechanical components should be in smooth working 
order. A new lamp of the type required for the test should be selected. 
This should be well constructed and free of any obvious defects, ready for 
seasoning. 

Calibration of lamp and photometer. An acceptable lamp of the desired 
size and service should be seasoned and calibrated at a definite current 
value. It should also be calibrated for intensity in a horizontal direction, 
as indicated by permanent orientation-reference markings (fiducial lines) 
placed on the bulb. 

The calibration data of the lamp consist of three items : 

Manufacturer's light output rating in lumens. 

Fiducial intensity in candlepower. 

Input in amperes and volts. 

Having the fiducial intensity in candlepower and the rated output in 

lumens, the numerical ratio between the total bare lamp output in lumens 

and the intensity in the marked direction is independent of the current 



* For projector-type luminaires only. 

t This method of test luminaire selection is applicable particularly to types with diffusing glass ware. 



THE MEASUREMENT OF LIGHT 



5-17 



, 



TYPICAL DIMENSIONAL 


MEASUREMENTS FOR 






LUMINAIRES 




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(PHOTOGRAP 


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Photometric Data 



LUMINAIRE DISTRIBUTION DATA 


ANGLE 


pSmr E " 


s 


180 


S-/S 




175 


v?7 


f? 


165 


■7JS~ 


'*J 


155 


V 3J 


X°l 


145 


jyj 


3 is 


135 


3.6 3 


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125 


2&7 


/ r° 


115 


7}f 


>n 


105 


76 


t/ 


95 


3f 


vi 


90 


iZl 




85 


*?<, 


323 


75 


rs° 


-}°t 


65 


/C'° 


IS ?F 


55 


2)1, 


2I2L 


45 


1?J° 


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35 


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25 


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17 Si 


15 


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K^wluSSSe*:'!?:'. 



MAXIMUM BRIGHTNESS OF LUMtNA1R£ 


ZONE 


s 


S.DES* 


END 






7^/5- 




0-30° 








30-60° 








60-90° 








70° 




///- 













E_<3f«/,-'-f>X 



./*V«-... APPROVED BV.^.-t 



a b 

FIG. 5-9a. Page from standard I.E.S. report form showing dimensioned scale 
drawing and photograph, b. Distribution data presented on standard I.E.S. 
Form. 

or voltage at which the lamp is held. This is the basis of the following 
method for obtaining the output and distribution characteristics of the 
luminaire. 

The lamp can be used as an absolute standard of intensity, but for the 
purpose of these tests it is better to use it as a combined standard and test 
lamp. The lamp is held at a definite current value rather than voltage 
value throughout the test to eliminate possible errors due to socket drop or 
faulty electrical connections. 

The lamp is first used to calibrate the photometer with which the lu- 
minaire is to be tested. Since the intensity of the lamp in the marked 
direction is related by a fixed numerical ratio to the total output of the 
lamp in lumens, regardless of the current at which the lamp is held, it is 
possible to calibrate the photometer by light received from the bare lamp 
in the marked direction, as though the lamp was operated to give rated 
intensity. Since the lamp is held at the same current throughout the 
standardization and the test, luminaire characteristics determined will be 
the same as if the lamp were held at rated lumen output throughout the 
test. 

Any ammeter of good constancy and giving a large scale deflection for 
the current measured is satisfactory. The exact meter calibration need 
not be known. In general, it is best to hold the current about 5 per cent 
less than the calibration current in order to ensure minimum change of 
light output from the lamp during the test. The selected current must 



5-18 I E S LIGHTING HANDBOOK 

be carefully maintained throughout the test. By calibrating the photom- 
eter directly against the test lamp, regardless of the exact candlepower 
at which the lamp is held, illumination values are obtained in terms of the 
standardization values of the lamp. 

The standard lamp is placed at a measured distance D (feet) from the 
photometer head, so that the illumination received by the photometer 
plate is that established by the fiducial lines on the bulb. The assumed 
illumination is then 

E = — footcandles 

where / is the standardized fiducial intensity in candles. This value of E 
is used to find the scale constant C of the photometer. When the scale 
reading is S, 

C X 8 = E 

The standard lamp is then adjusted in the luminaire and connected with 
the same ammeter as used for the calibration. The photometric test is 
carried on at the selected current. 

The actual values of light output and beam intensities under these 
conditions will be smaller than they would be if the lamp were operated at 
normal rating, but this method of calibrating the photometer exactly 
compensates for the difference, and the photometer readings times the 
constant C give values correct for rated lumens output. 

Adjustment of lamps in the luminaire. The exact position of the light 
center of the lamp in the luminaire is extremely important in the case of 
projector-type devices such as floodlights and searchlights and may exert 
a considerable influence on the characteristics of general lighting lumi- 
naires. Therefore, before making any photometric measurements, the 
lamp should be carefully adjusted in the luminaire. 

For projector-type luminaires the focusing of the lamp is to be done at a 
distance of 100 feet or more from the observing screen, and at the same 
distance at which the photometer readings are to be taken. The lamp 
should be adjusted to give the narrowest uniform and symmetrical beam.* 

Whenever the adjustment of the lamp in a projector -type luminaire is 
not fixed by the design or specified by the manufacturer, the lamp shall 
be adjusted as follows: (a) The filament opening of a ring-type filament, 
such as the C-5 or C-7A, shall be toward the front or up. (b) The lead 
wires of a monoplane-type filament, such as the C-13, shall be placed paral- 
lel to the plane of the reflector opening and away from the reflector. 

For general lighting luminaires in which there is provision for adjustment 
of the light center of the lamp, the position should coincide with that 
stated by the manufacturer or shown on the manufacturer's plan. 

Photometric tests for general lighting luminaires. If the luminaire is 
regularly sold or recommended by the manufacturer to be used with a 
particular fitting such as a support, the fitting should be attached during 

• Unless another working focus is specified. 



THE MEASUREMENT OF LIGHT 5-19 

the test and described in the report. If no such device is provided or 
recommended in the manufacturer's literature, the following conditions 
shall apply: (a) For enclosing globes, the opening shall be covered by a 
material having a neutral tint, a mat surface, and a luminous reflectance 
of 30 per cent to 40 per cent; no other reflectance is acceptable. The 
report shall state the exact value of the reflectance, (b) The cap-contact 
position (i.e., the distance from the cap-contact of the lamp to the plane 
of the fitter screw) shall be 1| inch for the 4-inch fitter, 2 inches for the 
6-inch fitter, and 3 inches for all mogul-base lamps, unless some other 
position is specified by the manufacturer of the globe and is stated in the 
report. 15 

The total lumen output of each of the six samples shall be measured in a 
sphere or by an equivalent method. (See page 5-26.) The results 
shall be stated in the report as the per cent of total bare lamp lumens. 

The candlepower distribution characteristics of the sample whose lumen 
output is closest to the average output of the heaviest, the lightest, and 
three of average weight shall be determined : (a) the candlepower at 
degree of the bare lamp and the luminaire, (b) the candlepower of the ro- 
tating luminaire at 5 degrees, 10 degrees, 15 degrees . . ., and 175 degrees. 

Note: If it is not feasible to rotate a luminaire with symmetric distribu- 
tion, readings should be made in at least eight planes and averaged. Meas- 
urements should be made in planes spaced at not less than 5 -degree in- 
tervals for those luminaires with asymmetric distributions. 

The test distance in all cases shall be not less than 10 feet, or five times 
the maximum dimension of the luminaire, whichever is larger. 19 

The maximum brightness of the luminaire in footlamberts in each of 
the following zones (at both sides and ends where asymmetric) shall be 
determined with a suitable photometer: degree, degree-30 degrees, 
30 degrees-60 degrees, and 60 degrees-90 degrees. The angle at which 
the maximum occurs shall be recorded in each case. The photometer or 
diaphragm should be so adjusted that the projected area observed is 
approximately one square inch. When there is symmetry in a zone, the 
lumiiiaire should be rotated during the measurements. 

Photometric tests for projector-type luminaires. The whole aperture of 
projector-type luminaires such as locomotive headlamps, aircraft landing 
lamps, airway beacons, floodlights, and searchlights is usually filled with 
light and appears equally bright all over. This aperture area is therefore 
the source for photometric purposes. Measurements are expressed in 
terms of apparent candlepower measured at a specified distance. It is 
common to determine maximum apparent beam candlepower, lumen 
output in the beam, and angular beam spread (both horizontal and ver- 
tical). 

Mounting luminaire. So that the directions of the beam may be ad- 
justed vertically or horizontally or in both directions at will, the luminaire 
should be so mounted that the beam can be adjusted in accurate vertical 
and horizontal steps not greater than 0.1 degree. 



5-20 I E S LIGHTING HANDBOOK 

Test distance. Accurate results in testing projector -type luminaires 
can be obtained only if the test distance is adequate. A minimum range 
of 100 feet is recommended for floodlights, and for searchlights much greater 
distances are often necessary as indicated by Fig. 5-10. 

Test procedure. Beams produced by projector -type luminaires are 
likely to be nonuniform in intensity. Traces of filament images are almost 
always detectable and, particularly in the case of devices which utilize 
carefully figured specular mirrors, the images may be quite sharp. Errors 
may be caused by these filament images if individual photometric observa- 
tions cover too small an area at the proper test distance. A device such as 
a sphere, diffusing screen, or test plate capable of integrating the illumina- 
tion of a square subtending one degree on each side may be used to mini- 
mize these errors. ' (Note: 20.94 inches subtends one degree at 100 feet.) 

The luminaire should be adjusted in ten equal angular steps in each of 
ten equally spaced vertical or horizontal planes. The spacing should be 
planned so that the maximum beam candlepower is approximately centered 
and so that 10 per cent of maximum is just within the area covered. The 
illumination should be measured for each of the 100 settings and plotted 
on rectangular co-ordinates as shown in Fig. 14-4c. The candlepower in 
the beam may be computed using trie zonal constants found in Appendix 
Table A-31, page A-47. 

Correction for atmospheric transmission. The absorption of light by 
moisture, smoke, or dust particles even in an apparently clear atmosphere 
may introduce considerable errors in measurements made at test distances 
greater than 100 feet. 16 ' 20 It is therefore desirable to measure the atmos- 
pheric transmission before and after the test has been made. This may 
be done by measuring the illuminations at two distances (500 feet and 
1,000 feet, for example). When the absorption is not great an approxi- 
mate correction can be calculated by assuming that the difference between 
the two values of candlepower computed by means of the inverse-square 
law, divided by the difference in distance, equals the absorption per foot. 

General Photometric Methods 

Substitution. By the use of the substitution method, in which a third 
source whose luminous intensity must be constant (but need not be known) 
is used as a comparison lamp on one side of the photometer head while 
sources to be compared are placed in turn on the other side, the luminous 
intensity of the comparison lamp is cancelled out and the ratio of test 
source candlepowers is obtained independent of any lack of symmetry in 
the photometer. Usually, the distance between the photometer head 
and comparison lamp is fixed, so that the brightness of the comparison 
surface is constant. 

Heterochromatic visual photometry. Close attention to detailed photomet- 
ric procedure is required in the photometry of discontinuous spectra such 
as are produced by discharge sources. 



THE MEASUREMENT OF LIGHT 



5-21 



1,000 

800 



2 400 
5 300 



























































































































DIAMETER OF 
PARABOLIC 
REFLECTOR 
























,60 INCHES 




































\\ 






















\ 










48 


















\ 


























\ \ 


































>s^ 


■v36 
0^< 




















v 






24 






















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V 


\18 
16 > 





















0.1 0.2 0.3 0.4 0.5 0.6 0.7 0-8 0.9 1.0 1.1 1.2 1.3 1.4 
DIAMETER OF DISK TYPE LIGHT SOURCE IN INCHES 

FIG. 5-10. Relationship between minimum photometric test dis- 
tance, light source diameter (disk type), and parabolic mirror diameter 
(12-inch to 60-inch) for accurate measurement of central intensity in 
a searchlight beam. 

It is necessary to standardize the observing conditions so that results are 
reproducible. As far as possible, the conditions under which the visibility- 
data defining the standard observer were obtained should be duplicated. 
A small field is required to limit observation to the macula, a small sensitive 
region near the center of the retina filled with closely packed cones, the 
light sensitivity of which corresponds approximately to published visibility 
data. The rods found in the regions surrounding the macula are relatively 
more sensitive to weak illumination and they have a peak light sensi- 
tivity at shorter wavelength than the photopic or standard sensitivity. 
These differences between the location and the brightness sensitivity of 
the retinal rods and cones give rise to the Purkinje effect and may lead to 
serious photometric errors if overlooked. (See page 2-3.) 

These problems are important whenever sources such as the mercury, 
sodium, or neon lamps are to be photometered, and methods have been 
developed whereby good results may be obtained through the use of color 
filters. 21 It has been found that amber filters can be designed to match 
sunlight, daylight, or skylight with tungsten source illumination. The 
light from the Welsbach mantle is matched by tungsten illumination modi- 
fied by a light green filter. Carbon arc lamps can be photometered with 
the aid of amber filters on the test side or blue filters on the comparison 
side. Blue-green radioactive luminous materials can be color-matched 
with tungsten by means of a blue-green filter on the tungsten side. Filters 
may also assist in the visual photometry of fluorescent sources. 

All exact or approximate color-temperature colors can be matched by 
the use of color-temperature-altering filters and by the adjustment of the 



5-22 I E S LIGHTING HANDBOOK 

comparison lamp color temperature. The design and selection of such 
niters has been described. 22 These niters are rated in terms of their color 
temperature altering power; which, for convenience in computing, is 
developed on the scale of reciprocal color temperature on which the custo- 
mary unit is the micro-reciprocal degree, abbreviated for convenience to 
"mired." One mired is about the smallest observable color temperature 
difference and the customary scale ranges from 50 mireds (20,000 degrees) 
to 1,000 mireds (1,000 degrees). The Macbeth illuminometer has a 
comparison lamp which can be conveniently adjusted from about 410 
mireds (2,440 degrees) to 470 mireds (2,130 degrees). Through the use 
of a series of color temperature raising and lowering filters covering the 
entire scale with the interval between any two adjacent niters less than 60 
mireds, sources throughout the whole range of color temperature can be 
photometered. If a specific color temperature is desired the Davis-Gibson 
filters can be prepared. 23 

Because the use of filters with sources having a widely different energy 
distribution produces only a psychological color match, the procedure by 
which standard and test lamps are in turn photometered against a com- 
parison lamp is not a true substitution method and therefore is not a satis- 
factory safeguard against photometric error. The transmittance and re- 
flectance of various components of the photometer are usually different 
for the test, standard, and comparison source energy distributions. In 
fact, the eye itself is not symmetrical in light sensitivity about its optical 
axis, and for the most precise measurements it may be necessary to rotate 
the photometer about its vertical axis so as to interchange the positions of 
the field images on the retina. When this procedure is followed, the aver- 
age of the two sets of readings should be used. 

The magnitude of the necessary corrections for variable absorption can 
be reduced by taking steps to ensure that the photometer is as nonselec- 
tive in its absorption characteristics as possible. 

The test plate reflectance should also be nonselective, having as high 
reflectance as practicable confoiming closely to the cosine law of perfect 
diffusion. White opal glass and white blotting paper make reasonably 
good test plates with luminous reflectance of approximately 80 per cent. 
The blotter may introduce a small specular error and is more likely to be 
soiled. Observations should be made normal to the test plate. When 
this is not possible, the reflectance characteristics of the plate should be 
detei mined in advance and readings at the angle of reflection of the prin- 
cipal sources should be avoided. 

For measuring the color temperature of light sources, color temperature 
standards have been made available both by the National Bureau of 
Standards* and by the Electrical Testing Laboratories. t Comparisons 
with them may be made either visually by matching the test lamp against 
the standard, or, photoelectrically, by comparing the red-to-blue ratio of 
the test lamp with that obtained for the standard using the same filters. 

* Washington, D.C. 
t New York, N.Y. 



THE MEASUREMENT OF LIGHT 5-23 

Photometric Instruments and Their Use 

Photometry dates back to the early 1700's. Bouguer in 1729 first 
compared two sources (one a reference standard) by allowing their light 
to fall upon two contiguous white surfaces, each receiving the light from 
only one source. Either one or the other source was moved until the 
brightnesses of the two surfaces appeared to be the same. 

The Bunsen disk consists of a translucent paraffined spot in the center 
of a substantially opaque white paper flanked by two mirrors forming an 
angle of 90 degrees bisected by the paper. From a point in the plane of 
the paper, images of both sides of the paper formed by the mirrors can be 
seen at one time. With the light sources placed on either side of the disk, 
a photometric balance is made by comparing the two reflected images of 
the paper. To secure a balance the distance from one or both light sources 
to the disk is adjusted. 

The Leeson disk is a star cut in white opaque paper covered with thin 
tissue paper. In all other respects it is the same as the Bunsen disk but 
provides slightly increased accuracy. 

The Lummer-Brodhun cube consists of two identical 45 to 90 degree 
prisms with a pattern (usually a small circle) etched in the hypotenuse face 
of one. The two hypotenuse faces are pressed together to make optical 
contact. Where the surfaces are in optical contact, light is transmitted, 
thus presenting an opportunity to compare two fields. More accurate 
results may be obtained than with either Bunsen or Leeson disks. 

The more precise contrast Lummer-Brodhun cube is a refinement over 
the simple cube. With the simple Lummer-Brodhun cube a photometric 
balance (brightness match) is secured when the two fields illuminated 
by the standard and the test source, respectively, merge and the lines 
of demarcation disappear. In the contrast cube, a balance is secured 
by matching one contrast field centered in an outer field with another 
contrast and outer field. The contrast fields are in the center of each 
of the simple fields and their brightness is about 8 per cent less than the 
brightness of the simple fields. This arrangement results in slightly in- 
creased precision; however, it is necessary to use very closely color matched 
standard and test sources if precise results are to be obtained. 

The flicker photometer was the first instrument by means of which sources 
not identical in color could be compared satisfactorily. 25 Its use is com- 
plicated by the fact that a color response calibration must be determined 
for each different observer. Also, the test and comparison fields must be 
surrounded with a brightness substantially equal to the test field bright- 
ness. Quite accurate determinations of intensities from light sources of 
different color characteristics are obtainable with this instrument. 

The Marten's polarization photometer is a laboratory device designed 
to operate in accordance with the tangent-squared law of polarization. 
This involves the production of polarized images of two surfaces by means 
of a Wollaston prism. The images are polarized in planes perpendicular 



5-24 I E S LIGHTING HANDBOOK 

to each other. An analyzing Nicol prism interposed in the path of these 
beams will reduce one image by the factor cos 2 9 and the other by the factor 
sin 2 6, where 6 is the angle between the polarizing plane of the Nicol prism 
and the plane of polarization of the light forming the first image (plane of 
polarization of the ordinary ray transmitted by the Wollaston prism). 
If 6 is the angular position for a photometric balance, the ratio of the 
brightnesses of the two images, with no Nicol prism interposed, would be 
tan 2 6. 

The physical photonteter has been available since about 1925. Three 
types are common: the barrier-layer cell which generates a current when 
exposed to light, the resistance cell which changes its resistance when 
exposed to light, and the phototube of which saturation current at any 
voltage is a function of the illumination. A thermopile photometer also 
has been developed. 9 Some cells have undesirable lag and fatigue char- 
acteristics. 

A wide range of sensitivities and responses may be secured through the 
use of either resistance cells or photoelectric tubes. For short wavelengths, 
such as the ozone-producing region around 0.185 micron, platinum photo- 
tubes can be used. For the germicidal range around 0.25 micron, tantalum 
or tungsten phototubes can be used. For the erythemal band, sodium 
cells are available, and in the infrared, silver cesium oxide and thallous 
sulphide tubes are useful. 

A sector disk w T ith an adjustable angular aperture can be rotated between 
a source and a surface so that the light from the source reaches the sur- 
face for only a certain fraction of the time, and if the rotation is so fast 
that the eye perceives no flicker the effective brightness of the surface is 
reduced in the ratio of the time of exposure to the total time (Talbot's 
law) . The reduction is by the factor 0/360 degrees, where 6 is the angular 
aperture in degrees. The sector disk has advantages over many filters 
in that it is not affected by a change of characteristics over a period of time 
and reduces total luminous flux without changing its spectral composition. 

Neutral filters are not readily obtainable. Wire mesh or perforated 
metal filters although perfectly neutral have a limited range. Mirrored 
filters have high reflectance and the reflected light must be controlled to 
avoid errors in the photometer. Also, it is difficult to secure completely 
uniform transmission over all parts of the surface. 

So-called neutral glass filters are seldom neutral. In general, they have 
a characteristic high transmission in the red region and low in the blue. 
This may be reasonably well corrected by the use of two layers of glass, 
one of the most neutral glass available and the second yellow-green which 
absorbs in the extreme red. However, this type of filter has a transmit- 
tance characteristic curve which varies with ambient temperature as do 
the curves for many other optical filters. 

The "neutral" gelatin filters are quite satisfactory, though not entirely 
neutral and some have a small seasoning effect, losing neutrality over a 
period of time. These must be protected by being cemented between two 
glass surfaces and watched carefully for loss of contact between the glass 
and gelatin. Any separation changes the transmittance characteristics. 



THE MEASUREMENT OF LIGHT 



5-25 





FIG. 5-11. Distribution or gonio photometer used at 
the Electrical Testing Laboratories for obtaining candle- 
power distribution curves. The luminaire mount is so 
arranged that symmetrical luminaires may be rotated 
about a vertical axis during the measurements. 

A distribution (gonio) 'photometer such as that shown in Fig. 5-11 is 
used to determine the candlepower distribution curve of light sources and 
luminaires and the reflectance characteristics of materials. 26 Many have 
provision for rotating the source (or placing it in various orientations) 
and carry one or more mirrors on arms moving about the source as a center. 
The "candlepower distribution curve" and the total flux of luminaires 
may be determined by measuring the luminous intensity at the middle of 
each 10-degree zone from to 180 degrees; angles customarily being 
measured counterclockwise with the nadir or zero at the bottom or "six 
o'clock" position. If, then, the mean mid-zone luminous intensity* for 
each 10-degree zone is multiplied by a zone factor, which is the zonal area 
on unit radius sphere, total lumens for any zone or the complete sphere 
(total flux) can be computed as can the efficiency of the luminaire. Zone 
factors are given in Appendix Table A-30 page A-45. 

Several integrating (sphere) photometers have been constructed but the 
one most generally used is the Ulbricht sphere of the type shown in Fig. 
5-12. These have been used in dimensions from an inch or so to 15 feet 
in diameter. The size is principally a matter of convenience. With 
proper precautions and corrections, a small sphere can be quite as accurate 
as a large one. A cube or octahedron has also been used. The limiting 
minimum dimension is the size of the luminaire, and the correction de- 
creases as the size increases. 27 



* In some cases mean zone intensity may occur at other than mid-zone angle. 



5-26 



I E S LIGHTING HANDBOOK 




FIG. 5-12. Fifteen-foot integrating (Ulbricht) sphere 
used at the National Bureau of Standards. 

A hollow sphere with a diffusely reflecting inner surface integrates light, 
either from a source within the sphere or from a beam projected through 
an aperture into the interior. Every part of the sphere reflects to other 
parts of the sphere. Therefore, there are two components of light, that 
direct from the source and that reflected from the sphere wall. If the light 
direct from the source is cut off, then the reflected light is proportional to 
the total light output of the source. The brightness of a small area of the 
sphere wall, or the brightness of the outer surface of a diffusely transmitting 
window in the sphere wall, is compared with that of a comparison surface 
by means of a photometer. Alternative methods are to measure the illu- 
mination of a test-surface a fixed distance from the outer surface of the 
sphere window or of a test-surface built into the inner surface of the sphere 
wall. The window or area is screened from direct light from the source, 
but receives light by reflection from the other portions of the sphere. 
The various elements of uncertainty entering into the considerations of a 
sphere as an integrator make it undesirable to use a sphere for the absolute 
measurement of flux but do not detract in the least from its use when a 
substitution method is employed. 

Spectrophotometers 

In spectrophotometers the light is spectrally dispersed by a device 
such as a prism or grating. (See Fig. 4-14, page 4-25.) Incorporated in 
the instruments is a visual or photoelectric photometer by means of which 
the reflectance or transmittance of the test material at each of many nar- 



THE MEASUREMENT OF LIGHT 5-27 

row wavelength bands is determined. The reflectance or transmittance 
for light of known spectral distribution may then be calculated by use of 
the luminosity factors for the "average eye" (standard I.C.I, observer). 
The factor is computed from the relation 

r> _ 2 U\ K\ R\ 
~ 2 UxKx 

where R is the desired luminous reflectance, and U\ is the energy of wave- 
length region X, incident on the sample K\ is the standard luminosity 
factor for wavelength X, and R\ is the reflectance as determined by a spec- 
trophotometer for wavelength X. The summation is usually carried out 
in every 0.01 -micron band from 0.380 to 0.760 micron. 28 

Electrical Measurements 

It is often necessary to determine certain electrical characteristics of 
light sources and accessories in connection with photometric measurements. 
The following are the measurements most commonly encountered. If 
additional information is required the reader is referred to one of the many 
texts or handbooks on electrical engineering. 29 

Power: (1) Direct-current circuits. Power is the product of the voltage 
and the current. It may be measured by using a voltmeter and ammeter 
or by using a wattmeter. 

The ammeter or current circuit of the wattmeter is connected as shown 
in Fig. 5-13a at A and the voltmeter or voltage circuit of the wattmeter 
is connected as shown at V. With the switch S open the reading of the 
ammeter or wattmeter is taken. With the switch S closed readings of 
both ammeter and voltmeter or of the wattmeter are taken. The readings 
with $ open give the current taken by the voltmeter (when using ammeter 
and voltmeter) or the power taken by the wattmeter voltage circuit. 
The readings with S closed give the current taken by the voltmeter plus 
the load current (when using ammeter and voltmeter) or the power taken 
by the wattmeter voltage circuit plus the load power. 

The power taken by the load is then 

(I — I v ) E = Wl for ammeter -voltmeter method, or 
W — W v — W L for wattmeter method, 

where / is the ammeter reading with S closed (the current through the 
voltmeter plus the load current) ; I v is the ammeter reading with S open 
(the current through the voltmeter) ; E is the voltmeter reading; W is the 
wattmeter reading with S closed (the power taken by the wattmeter volt- 
age circuit plus the power taken by the load ) ; W v is the wattmeter reading 
with S open (the power taken by the voltage circuit of the wattmeter) ; 
and W L is the power taken by the load. 

A compensated wattmeter is one that is so designed that the current 
through the compensating coil produces a torque equal and opposite to 
that produced by the power taken by the wattmeter. The current and 



5-28 I E S LIGHTING HANDBOOK 

voltage circuits must be connected as shown in Fig. 5-13a. As a check on 
the correctness of connections the compensated wattmeter should read 
zero when S is open (i.e., the load is not connected). 

Power: {2) Alternating-current circuits. The power (W) in an alter- 
nating current circuit is the triple product of the voltage (E), the current 
(/), and the power factor (cos d) : 

W = EI cos d 

If the power factor is known, the procedure just outlined for direct- 
current measurements may be followed (using instruments designed for 
alternating-current operation). When the power factor is not known, 
the ammeter-voltmeter method can not be employed. Alternating-cur- 
rent wattmeters, however, will indicate the power. 

Power factor. If an alternating-current wattmeter is not available a 
voltmeter may be used to determine the angle 6 of which the cosine equals 
the power factor. The circuit is given in Fig. 5-136. Simultaneous read- 
ings are taken on three voltmeters or readings in rapid succession on a 
single voltmeter. R is an auxiliary noninductive resistor chosen to give a 
reading of about or above one quarter full scale. The readings are then 
used to determine graphically the angle 6. By convention Vi is drawn 
horizontally, the length being proportional to the voltmeter reading V\. 
An arc of radius proportional to V2 is drawn with the right-hand end of Y\ 
as a center, and an arc of radius proportional to Vz is drawn with the left- 
hand end of Vi as a center. These arcs intercept at some point B. V\ 
is extended to the right. The angle BAC is then the desired angle 0, 
called the angle of lead or lag or simply the power factor angle. The cosine 
of 8 is determined from tables or by taking the ratio of the length of AC 
to the length of A B. 

Voltage. The voltmeter should be connected as close to the load, (or 
circuit component) to be measured as possible to avoid including in the 
measured voltage any voltage drops in other parts of the circuit. A 
voltmeter connected as shown by the dashed lines in Fig. 5-13c measures 
the voltage across the load plus the voltage drop across the resistor R, 
whereas one connected as shown by the solid lines measures the voltage 
across the load alone. Voltmeters are connected "across the line," that 
is, in parallel or shunt connection with the circuit to be measured. 

Current. The ammeter should be connected in series with the load of 
which it is desired to measure the current. An ammeter connected as 
shown by the clashed lines in Fig. 5-13d will measure the sum of the cur- 
rent in the dashed-line load and that in the solid-line load, whereas, one 
connected as shown by the solid lines measures the current to the solid- 
line load alone. 

Ammeters are not connected across the line. They are to be connected 
in series with the load. 



THE MEASUREMENT OF LIGHT 



5-29 




FIG. 5-13a. Meter connections for measurement of power in light source circuits. 
6. Method of connecting three voltmeters and graph for determining power factor 
of a lighting circuit, c. Voltmeter connections for measurement of volts in light 
source circuits, d. Ammeter connections for measurement of current in light source 
circuits, e. Test circuit for preheat-starting (hot-cathode) type fluorescent lamps. 

Test circuit for fluorescent lamps. The circuit shown in Fig. 5-13e 
is a convenient arrangement for determining the electrical characteristics 
in a preheat-starting (hot-cathode) type of fluorescent-lamp circuit. 

Precautions. Only one meter at a time is to be connected in the lamp 
circuit. The ammeter or current circuit of the wattmeter should have a 
resistance such that the drop across it is less than 2 per cent of the lamp 
voltage. The voltmeter or voltage circuit of the wattmeter should have 
as high a resistance as possible with reliability; this should be at least 
1,000 ohms per volt. The phase angle correction is negligible when only 
one instrument is connected in the lamp circuit. Correction or compen- 
sation for the voltage drop in any series elements of meters should be made 
unless they are less than \ per cent of lamp volts. 

With a lamp in the circuit and with Si open and $2 closed the corrections 
for the current in the voltmeter or power loss in the wattmeter can be 
determined. With Si closed and *S 2 open the lamp is started and operated 
for about 10 minutes to allow conditions to become nearly constant before 
any measurements are made. A refinement of method is to place a foot- 
candle meter against the lamp or place the lamp on a photometer and 



5-30 



I E S LIGHTING HANDBOOK 



determine the light reading with no electric meters in the circuit and to 
adjust the line voltage to re-establish this reading when any meter is 
connected in the lamp circuit. 

REFERENCES 

1. Meyers, G. J., Jr., and Mooney, V. J., "Measuring the Brightness of Streets by Means of Photography," 
Ilium. Enq., June, 1941. Dean, J. H., "A Graphical Method of Computing Street Lighting Illumination 
Charts," ilium. Eng., July, 1942. Davis, D. D., Ryder, F. A., and Boelter, L. M. K., "Measurement of 
Highway Illumination by Automobile Headlamps under Actual Operating Conditions," Trans. Ilium. Eng. 
Soc, July, 1939. 

2. Committee on Lighting Practice of thel.E.S., Report of, "Recommendations for a Standard Method for 
Measuring and Reporting Illumination from Artificial Sources in Building Interiors," Ilium. Eng., February, 
1943. 

3. "Procedure for Measuring Footcandles of Floodlight Installations," National Electrical Manufacturer's 
Association Standards Bulletin PL, November, 1939. 

4. Forsythe, \V. E., "The Present Status of Photometry," Trans. Ilium. Eng. Soc, February, 1936. 

5. "Report of the Committee on Portable Photoelectric Photometers," Trans. Ilium. Eng. Soc, April, 1937. 

6. Fogle, M. E., "New Color Corrected Photronic Cells for Accurate Light Measurements," Trans. Ilium. 
Eng. Soc, September, 1936. Dows, C. L., and Allen, C. J., "The Light-Meter and its Uses," Trans. Ilium. 
Eng. Soc, July, 1936. 

. 7. Parker, A. E., "Measurement of Illumination from Gaseous Discharge Lamps," Ilium. Eng., November, 
1940. 

8. Dows, C. L., "Illumination Measurements with Light Sensitive Cells," Ilium. Eng., February, 1942. 

9. Teele, R. P., "A Physical Photometer," J . Research Nat. Bur. Standards, September, 1941. 

10. Goodbar, I., "New Procedure to Measure Accurately Illumination at Large Angles of Incidence with a 
Barrier-Layer Cell," Ilium. Eng., November, 1945. 

11. "E.eport of the I.E. S. Sub-committee on the Measurement and Evaluation of Ultraviolet Radiation," 
Trans. Ilium. Eng. Soc, September, 1933. Benford, F., and Howe, R. F., "Energy Measurements in the 
Visible and the Ultraviolet," Trans. Ilium. Eng. Soc, March, 1931. Taylor, A. H., and Holladay, L. L., 
"Measurement of Biologically Important Ultraviolet Radiation," Trans. Ilium. Eng. Soc, September, 1931. 
Sharp, C. H., and Little, W. F., "The Problem of the Definition and Measurement of the Useful Radiation 
of Ultraviolet Lamps," Trails. Ilium. Eng. Soc, September, 1931. 

12. Catalog E-72, Leeds & Northrup Company, Inc., Philadelphia, Pennsylvania. 

13. Taylor, A. H., Brightness and Brightness Meters," Illu?n. Eng., January, 1942. " A Brightness Meter 
Developed by Luckiesh and Taylor," Lighting News, Trans. Ilium. Eng. Soc, March, 1937. 

14. Taylor, A. H., "A Simple Portable Instrument for Measuring Reflection and Transmission Factors in 
Absolute Units," Trans. Ilium. Eng. Soc, December, 1920. Baumgartner, G. R., "General Electric Light 
Sensitive Cell Reflectometer," Gen. Elec Rev., November, 1937. 

15. Committee on Lighting Service of the I. E. S., Report of, "Specifications for Testing Lighting Equip- 
ment, Section I, Specification No. C-l-1940, Luminaires for General Lighting," Ilium. Eng., March, 1940. 

16. "Testing Procedure for Narrow-Beam Enclosed Projectors," Trans. Ilium. Eng. Soc, May, 1936. 
"Photometric Testing Procedure for Searchlights," National Electrical Manufacturer's Association Standards 
Bulletin FL, December, 1944. 

17. Committee on Lighting Service of the I. E. S., Report of, "Specifications for Testing Lighting Equip- 
ment, Section II, Specification No. F-2-1941, Incandescent Filament Floodlights," Ilium. Eng., June, 1941. 

18. Committee on Lighting Service of the I.E.S., Report of, "Testing Specifications for Lighting Equip- 
ment, Section III, Asymmetric Show Window Reflectors," Trans. Ilium. Eng. Soc, June, 1933. 

19. Baumgartner, G. R., "Practical Photometry of Fluorescent Lamps and Reflectors," Ilium. Eng., 
December, 1941. 

20. Committee on Instruments and Measurements of the I.E.S., Annual Report of, "Part II — Description 
of Method for Measuring Atmospheric Transmission," Ilium. Eng., November, 1943. 

21. Little, W. F., and Estey, R. S., "The Use of Color Filters in Visual Photometry," Trans. Ilium. Eng. 
Soc, June, 1937. Johnson, L. B., "Photometry of Gaseous-Conduction Lamps," Trans. Ilium. Eng. Soc, 
June, 1937. 

22. Gage, H. P., "Color Filters for Altering Color Temperature Pyrometer Absorption and Daylite 
Glasses," J . Optical Soc. Am., February, 1933. 

23. Davis, R., and Gibson, K. S., "Filters for the Reproduction of Sunlight and Daylight and the De- 
termination of Color Temperature," Bureau of Standards, Misc. Pub., 114, 1931. 

24. Jones, L. A., "Summary of American Opinion on BS/ARP18, British Standard Specification for Fluo- 
rescent and Phosphorescent Paint," RC43, American Standards Association, New York, June, 1942. 

25. Kingsbury, E. F., "A Flicker Photometer Attachment for the Lummer-Brodhun Contrast Photom- 
eter," J . Franklin Inst., August, 1915. Guild, J., "A New Flicker Photometer for Heterochromatic Photom- 
etry", J. Sci. Instruments, March, 1924. Ferree, C. E., and Rand, G., "Flicker Photometry," Trans. Ilium. 
Eng. Soc, February, 1923. Moon, P., and Severance, D. P., "The Design of Photoelectric Flicker Photom- 
eters," Trans. Ilium. Eng. Soc, July, 1939. Sharp, C. H., and Kinsley, C., " A Practical Form of Photoelectric 
Photometer," Trans. Ilium. Eng. Soc, February, 1926. Sharp, C. H., and Smith, H. A., "Further Develop- 
ments in Photoelectric Photometers," Trans. Ilium. Eng. Soc, April, 1928. 

26. Dows, C. L., and Baumgartner, G. R., "Two Photo-voltaic Cell Photometers for Measurement of 
Light Distribution," Trans. Ilium. Eng. Soc, June, 1935. Colby, C. C., Jr., and Doolittle, C. M., "A Dis- 
tribution Photometer of New Design," Trails. Ilium. Eng. Soc, March, 1923. 

27. Weaver, K. S., and Shackelford, B. E., "The Regular Icosahedron as a Substitute for the Ulbricht 
Sphere," Trans. Ilium. Eng. Soc, March, 1923. Lectures on Illuminating Engineering, The Johns Hopkins 
Press, Baltimore, Maryland, 1911. 

28. Hardy, A. C, "A Recording Photoelectric Color Analyzer," J. Optical Soc. Am. and Rev. Scientific 
Instruments, February, 1929. Hardy, A. C., "A New Recording Spectrophotometer," J. Optical Soc Am., 
September, 1935. 

29. Knowlton, H. E., Standard Handbook for Electrical Engineers, Seventh Edition, McGraw-Hill Book 
Company, Inc., New .York, 1941. Pender, H., Del Mar, W. A., and Mcllwain, K., Electrical Engineers' Hand- 
book, Third Edition, John Wiley & Sons, Inc., New York, 1936. 



SECTION 6 
JLIGHT SOURCES 

It is known that man made use of the incandescent flame as a source of 
light even before the beginning of recorded history, and that more than 
half of the world's inhabitants and 10 per cent of American families use 
"flame sources exclusively even today. The present efficiencies of the 
"candle (0.1 lumen per watt), the kerosene lantern wick (0.3 lumen per 
watt), the acetylene flame (0.7 lumen per watt), and the illuminating gas 
flame have not changed greatly since they were first utilized for lighting 
purposes. 

The first electric arc was discovered by Davy in 1801. Edison's first 
successful incandescent lamp in 1879 emitted 2.6 lumens per watt. In 
1901 Cooper Hewitt's forerunner of modern gaseous discharge sources 
produced 13 lumens per watt. Thus by the time the Illuminating En- 
gineering Society was founded in 1906 a recognizable ancestor of each of 
our present-day sources, with the possible exception of the fluorescent lamp, 
had already been developed.* See Fig. 6-1. 



MAXIMUM THEORET- 
ICAL EFFICIENCY OF 
WHITE (EQUAL- 
ENERGY) LIGHT 




FIG. 6-1. A pictorial history of light source development and efficiency. 



* In 1898 Edison applied for a patent on a "Fluorescent Electric Lamp" which was issued to him in 1907 
as U. S. Patent No. F65.367. 

References are listed at the end of each section. 



6-2 



I E S LIGHTING HANDBOOK 



Lamp Life and Depreciation 

Rated lamp life is based on averages obtained from laboratory life- 
testing of large numbers of lamps. The normal "mortality" curve for 
incandescent lamps is shown in Fig. 6-2. Some lamps fail earlier than 
rated life, others last longer. A perfect mortality record would be one in 
which all lamps reached their rated life and then burned out. This is not 
to be expected in practice. 

The depreciation curve superim- 
posed on the normal mortality curve 
indicates that lamps which live sub- 
stantially beyond rated life have be- 
come relatively inefficient. From 
an economic standpoint they should, 
under many circumstances, be re- 
placed before burnout. From the 
normal mortality curve it will be 
seen that at the end of rated life 55 
per cent of the lamps remain burn- 
ing, but those remaining lamps will 
deliver only 6 to 8 per cent addi- 
tional lumen-hours. These addi- 
tional lumen-hours are the most ex- 
pensive because they are being ob- 
it is economical to remove lamps from 











i^DE 


LUM 
PREC 


=N:i: : .\v:v. : - 

ATION :'.:';'.•: 



































































20 40 60 80 100 120 140 160 
PER CENT OF RATED LIFE 

FIG. 6-2. Curve showing reduc- 
tion in light output during life of a 
200-watt general-service incandescent 
lamp superimposed on a typical in- 
candescent-lamp mortality curve. 



tained at decreased efficiency 

service whenever the point is reached at which the cost of energy consumed 
per million lumen-hours exceeds the average cost of light produced up to 
that time, including all charges for lamps, energy, labor, and so forth. 
The point beyond which it is not economical to burn old lamps is termed the 
"smashing point. (See Fig. 6-3). The area under this curve represents 

the total lumen-hours produced by 
an assumed installation of lambs. 
It is obtained by combining the mor- 
tality curve with the typical depre- 
ciation rate throughout life. The 
darker-shaded part indicates the 
logical smashing point region where 
for the particular set of conditions 
assumed it is more economical to 
install new lamps than to keep the 
old ones in service. The light- 
shaded area represents the zone of 
group replacement, that is, of re- 
lamping the entire installation at 
one time before the normal rate of 
burnout reaches its peak. 1 



O q; 80 

I- w 
D°- 

&Z60 
D _ 
O (A 
£ §40 



20 

























1 '•:.'- 


UN 
\ ° 


ECONOMICS 
PERATING 


\L 








t-: 

IV 
I: •.: 










GROUP 
REPLACEh 


dENT- 


I.\v 
I- - .- 




M 












i'-' v 

v.--. 

IV-': 




: 







20 40 60 80 100 120 140 I6< 
PER CENT OF RATED LIFE 

FIG. 6-3. Typical "smashing- 
point" curve obtained by combining 
a normal mortality curve with a 
typical depreciation-throughout-life 
curve. 



LIGHT SOURCES 



6-3 



Lamp Renewal Rate 

From the mortality curve the number of burnouts likely to occur within 
a given period can be computed for a large installation. In a new installa- 
tion few burnouts would be expected during the first several hundred 
hours. Approaching normal life, there would be many burnouts, necessi- 
tating frequent lamp replacement. Thus for a period of several lamp 
renewals per socket, the renewal rate first swings high, then low, and 
finally settles down to a steady rate, ; as in Fig. 6-4. The solid line repre- 
sents the total replacements; the dotted curves the first, second, and so on 
replacement per socket. This theoretical curve holds only for an in- 
finitely large installation. In practical installations the curve, because 
of the law of probability, is likely to be rather jagged, although the general 
shape would be the same. 2 




150 200 250 300 350 

AVERAGE LAMP LIFE IN PER CENT 



FIG. 6-4. Renewal rate curves applicable to all types of lamps. 



6-4 



I E S LIGHTING HANDBOOK 



THE INCANDESCENT LAMP 

/ 

The first consideration of lamp design is that a source produce light most 
economically for the service intended, or, in other words, that the best 
balance of over-all lighting cost in terms of lighting results is secured. To 
realize this objective in an incandescent lamp the following factors must 
be definitely specified: filament material, length, diameter, form, coil 
spacing, mandrel size (the mandrel is the form on which the filament is 
wound), lead-in wires, number of filament supports, method of mounting, 
proper vacuum or filling gas, gas pressure, bulb size, bulb shape, tempera- 
ture, and surface treatment (frosting, coating, silver or aluminum pro- 
cessing). (See Fig. 6-5.) Very careful production control is equally 



GAS 

The gas used in most lamps of 40 watts 
and above prevents rapid evaporation of 

the filament, permitting higher temper- 

atures which result in higher efficiencies. 
Usual gas is a mixture of nitrogen and 
argon. Some lamps for special services 
may use krypton or hydrogen. 

LEAD-IN WIRES 

These wires conduct the current to and from 

the filament. Copper is used- from base to stem 

press, and nickel from stem press to filament. 

STEM PRESS 

The glass and lead-in wires are sealed airtight 

at this point. Here the lead-in wire is a combina- --' 

"Hon of a nickel-iron alloy core and a copper sleeve 

(Dumet wire) having substantially the same co- / 

efficient of expansion as the glass. / 

EXHAUST TUBE . , / 

Through this tube, projecting beyond the bulb during 
manufacture, the air is exhausted and the bulb filled 
with inert gases. The tube is then sealed off. 




SUPPORT WIRES 

Molybdenum wires hold the filament in 

place; a minimum number reduces heat 

losses. 

BUTTON 

The glass is softened during assembly 
and the support wires stuck in it. It is 
supported by the button rod. 

MICA DISK 

The mica disk reduces circulation of hot gases 
into the neck of the bulb, protecting the stem 
press, stem, and socket from excessive tem- 
peratures when necessary. 

FUSE 

The fuse is designed to open the circuit if the 

filament arcs. By reducing sputtering of the 

metal, cracking of the bulb is prevented. It 

also protects the circuit and prevents blowing 

of the line fuses. 



C-17 FILAMENT 
■' ,-7 FILAMENT 

f' f SUPPORTS 

, LEAD-IN 
r SUPPORTS 



. GLASS BUTTON 
ROD 




-ARBOR WIRE 



•STEM PRESS 



SIDE VIEW 
OF MOUNT 






T TOP VIEW 


,C-9 FILAMENT / 


j,m.,£, w FILAMENT / 


\\ 


M-jf/- SUPPORTS 1 


t 


1 /L. LEAD-IN \ 




_jfr' SUPPORTS \ 




■4— GLASS BUTTON 




J | ROD 




Jr-ARBOR WIRE 




WSTEM PRESS 


/ 


\ 


SIDE VIEW 


OF K 


10UNT 




100- WATT, ROUGH - 
SERVICE LAMP, A-23 BULB 



100-WATT, VIBRATION- 
SERVICE LAMP, A-23 BULB 



FIG. 6-5. Construction of common types of incandescent lamps for: (a) general 
service; (b) rough service; (c) vibration service. 



LIGHT SOURCES 



6-5 



necessary to ensure adherence to these specifications. Uniformity of 
""wattage, efficiency, and life ratings is necessary if lamps are to give de- 
pendable service. 3 Typical filament forms are shown in Fig. G-G. 
IUII 






COILED 
COIL 



IV 




NO.I-ANY N0.5-ANY N0.6-ANY NO.7 

BASE DOWN 








N0.7A-ANY N0.9-ANY 



NO. I3D 
BASE DOWN 




oo o o oooo 
o ooo 

MONOPLANE BIPLANE 



\W± 



N0.22-ANY 



DIFFERENTIAL COIL 
LAMP FILAMENT FORMS 



FIG. 6-6. Typical incandescent filament types, designations, and usual 

burning positions. 

The Tungsten Filament 

The requirements for a suitable material for a lamp filament involve 
the following: 

Melting point and vapor pressure. Light output depends on filament 
temperature. An iron rod heated in a furnace will first glow a dull red, 
and then becomes brighter and whiter as its temperature is increased. 
Iron, however, melts at about 2,800 degrees Fahrenheit. Edison chose 
carbon as a filament because it has no melting point and vaporizes at 
6,510 degrees Fahrenheit, which is above the melting point of tungsten 
(6,120 degrees Fahrenheit) and of any other known element. Carbon was 
the only filament material used for about twenty-five years. 

To obtain satisfactory life performance, carbon lamps had to be oper- 
ated much below the point of vaporization because of the high vapor pres- 
sure of carbon and the consequent high rate of filament evaporation at 
incandescent temperatures. Osmium (melting point 4,890 degrees Fahr- 
enheit) and tantalum (melting point 5,250 degrees Fahrenheit), even 
though having melting points below the vaporization point of carbon, 
can be operated at higher temperatures for the same life since their 
vapor pressures and evaporation rates are lower. For a short period prior to 
the development of the tungsten lamp these metals were used as filament 
materials. Tungsten, first used in 1907 for lamp filaments, proved su- 
perior to all others because of its relatively high melting point and low 



6-6 



I E S LIGHTING HANDBOOK 



evaporation rate. Gas-filled lamps were introduced 4 in 1913, gas pressure 
being a practical means of retarding filament evaporation. 

Strength, and ductility.) Early tungsten lamp filaments (1907-1911) 
were pressed from metallic tungsten powder and were very fragile. They 
were acceptable commercially only because their lumen-per-watt rating 
was approximately three times that of the relatively rugged carbon fila- 
ments then in use. In 1910 a method was developed for making ductile 
or drawn tungsten wire having four times the tensile strength of steel. 5 

Radiation characteristics. Tungsten selectively radiates a relatively 
high percentage of energy in the visible region, producing a continuous 
spectrum approximating that of a theoretical "blackbody." 

The resistance of tungsten wire increases with its temperature, being of 
the order of twelve to sixteen times greater at filament operating tem- 
peratures than at room temperature as shown in Fig. 6-7. Theoretically, 




O 1,000 2,000 3000 4000 5000 6.000 

TEMPERATURE IN DEGREES FAHRENHEIT 

FIG. 6-7. Variation of tungsten filament resistance with temperature for 

various lamps. 

then, an overshooting of current, in terms of normal current, would be ex- 
pected at the instant lamps are turned on, in proportion to the ratio of hot- 
to-cold resistance. However, the reactance characteristics of the circuit 
rarely, if ever, allow this ratio to be reached. Table 6-1 gives the ratio of 
theoretical to actual current inrush as determined under laboratory con- 
ditions for several sizes of lamps. This aspect of lamp operation is im- 
portant in the design and adjustment of circuit breakers, in circuit fusing, 
and in the design of lighting circuit switch contacts. 



LIGHT SOURCES 



6-7 



Table 6-1. 



Effect of Hot-Cold Resistance on Current in an 
Incandescent Filament 

(Laboratory conditions) 





120-VOLT 

NORMAL 

CURRENT 

(amperes) 


THEORETICAL 

INRUSH: BASIS 

HOT-TO-COLD 

RESISTANCE 

(amperes) 


ACTUAL MAX. 

CURRENT 

INRUSH BY 

TEST 

(amperes) 


TIME FOR CURRENT TO 


LAMP 
WATTAGE 


Reach 

Max. Value 

(seconds) 


Fall to 

Normal Value 

(seconds) 


75 
100 
200 

300 

500 

750 

1,000 


0.625 

0.835 

1.67 

2.50 

4.17 

6.25 

8.33 


9.38 
13.0 
26.2 
40.0 
67.9 
101.9 
142.4 


7.2 
9.0 
17.2 
26.2 
45.7 
51.7 
65.2 


0.0004 
.0007 
.0008 
.0011 
.0014 
.0021 
.0031 


0.07 
.10 
.10 
.13 
.15 
.17 
.23 



Vacuum and Gas-Filled Lamps 

The vacuum type of lamp was the only type available until 1913 and 
vacuum construction is still employed in 110- to 125-volt lamps consuming 
less than 40 watts. Lamps of 40 watts and above in the 110-125 volt 
range are usually gas filled.* 

The bulb of an incandescent lamp is filled with gas to introduce pressure 
on the filament in order to retard evaporation. While the gas conducts 
some heat away from the filament, this is more than offset by the higher 
temperatures at which the filament may be operated. 

Inert gases, that is, those that do not combine chemically with the fila- 
ment lead-in wires and supports, must be used, and, other things being 
equal, the best gas is the one with lowest heat conductivity. Nitrogen was 
first used because of its lower cost, purity, and availability; argon was 
recognized as better than nitrogen in many ways but it was scarce and 
relatively expensive. Present-day lamps have an atmosphere of argon 
and nitrogen mixed in varying proportions depending on their type. 
Argon alone ionizes at normal circuit voltages and tends to arc between 
the lamp lead-in wires. 

The rate of evaporation of a metal when surrounded by a gas varies with 
the size of the molecule of the gas. Krypton gas has a lower heat conduc- 
tivity than either nitrogen or argon and if used for lamps would permit a 
20 to 25 per cent gain in efficiency over the present 40-watt lamp rating. 
This gain would be less for the higher wattage lamps. However, krypton 
is at present too expensive to be used for all general-service lamps since 
its use would increase the present cost of the lamp perhaps by a factor of 
two. Its use is practical today only in special types of lamps such as the 
small miner's cap lamps, w r here high efficiency has a high money value 
since it prevents excessive drain on the battery, permits the use of smaller 
bulbs, and reduces the over-all weight of apparatus required to produce a 
given number of lumen-hours. 



Vacuum lamps are known as type B. Gas-filled lamps are known as type C. 



6-S 



I E S LIGHTING HANDBOOK 



Hydrogen has high heat-conductivity and is therefore inefficient for 
lamps for most purposes. However, this characteristic is useful in lamps 
used for signaling purposes where quick flashing (cooling) is desired. (See 
Fig. 6-8.) 

POWER 
ON 

100 




TIME IN SECONDS 



FIG. 6-8. Incandescence and nigrescence characteris- 
tics of "quick flashing" and general service lamps. 

Table 6-2 shows thermal and luminous characteristics of several vacuum 
and- gas-filled lamps. The filament dissipates its energy by radiation be- 
yond the bulb, by conduction and convection of the surrounding gas, by 
conduction of the leads and supports, and by bulb absorption. By refer- 
ence to the "Gas Loss" column of the table it will be noted that the per- 
centage of gas loss increases rapidly as the wattage is decreased, the value 
for the 40-watt lamp being 20 per cent as compared with 6 per cent for the 
1,000-watt lamp. 

In manufacturing lamps, gas usually is introduced at about 70 to 80 
per cent of atmospheric pressure. Operated under normal conditions 
the pressure rises to about atmospheric pressure. A lamp operated at 
more than normal temperatures may develop higher than atmospheric 
pressure within the bulb. When a hard glass bulb is used or when a bulb 
may be cooled by artificial ventilation, such as in projector housings, the 
filament temperature (and thereby the efficiency) may be increased. 
When this is done, it is advantageous to increase the internal gas pressure 
in order to minimize the vaporization of the filament. See Fig. 6-9. 

Incandescent Lamp Life,j Light Output, Efficiency, and Voltage Relation- 
ships 

Operating data on twenty-two typical incandescent lamps are given in 
Table 6-3. An incandescent lamp of any given wattage and voltage 
rating may be designed to last a few hours or a few thousand hours. 
Lamps are available with life ratings throughout this range. For equal 
inherent quality, the shortest-life lamps of any given size and type have 
the highest lumen-per-watt ratings and the longest life lamps have the 
lowest lumen-per-watt ratings. For example, a photoflood lamp with 
rated life of six hours produces approximately 30 lumens per watt whereas 
lamps with a laboratory life of about 5,000 hours produce about 8 lumens 
per watt. 



LIGHT SOURCES 



6-9 



V 



Table 6-2. 



Luminous and Thermal Characteristics of Typical Vacuum 
and Gas-Filled Incandescent Lamps 



WATTS 


RADI- 
ATED IN 
VISIBLE 

SPEC- 
TRUM 

(per cent 
of input 
wattage) 


TOTAL 
FILA- 
MENT 

RADIA- 
TION 
BEYOND 

BULB 

(per cent of 

input 

wattage) 


GAS 

LOSS 

(per cent 

of input 

wattage) 


END 
LOSS 

(Loss by 
conduc- 
tion at 
Filament 

Ends) 
(per cent 
of input 
wattage) 


FILA- 
MENT 
HEAT 
CON- 
TENT 
(joules) 


HEAT- 
ING 
TIME TO 
90 PER 
CENT 
LUMENS 
(seconds) 


COOL- 
ING 
TIME TO 
10 PER 
CENT 
LUMENS 
(seconds) 


STROBOSCOP- 
IC EFFECT 
(Per cent of 
variation of 
light output 
from mean) 




60 

Cycles 


25 

Cycles 


6* 
10* 
25* 


6.0 

7.1 

8.7 


93.0 
93.5 
94.0 


— 


1.5 

1.5 
1.5 


0.25 
0.62 

2.8 


0.04 
.06 
.10 


0.01 
.02 
.03 


29 
17 
IP 


69 
40 

28 


40 f 

60fJ 

100ft 


7.0 

7.5 

10.0 


69.9 
80.8 
82.0 


20.0 
13.5 
11.5 


1.6 
1.2 
1.3 


2.5 
5.5 

14.1 


.07 
.10 
.13 


.03 

.04 
.06 


13 
8 
5 


29 
19 
14 


200f 

300 f 

500 1 

lOOOOf 


10.2 
11.1 
12.0 
12.1 


77.4 
79.8 
82.3 
87.4 


13.7 
11.6 

8.8 
6.0 


1.7 

1.8 
1.8 
1.9 


39.5 

80.0 

182.0 

568.0 


.22 

.27 
.38 
.67 


.09 
.13 
.19 
.30 


4 
3 

2 
1 


11 
8 
6 
4 



! Vacuum, t Gas filled, t Coiled-coil filament. 





140 
120 
100 
80 




























































































60 











012345678 

DISTANCE FROM LAMP BULB IN INCHES 

c 



ICO 

LL1' > 

#0100 

US 

Q 2 90 

Ut 80 



70 









ZONE OF MAXIMUM 

TEMPERATURE " V - A ^ 














si 


f^ 


^ — "* 


JUNCTION OF BRASS 5, 
AND GLASS ^*^T 












f ,' 




<< POINT OPPOSITE 
FILAMENT 




V 


/^ 

' 















40 SO 60 70 80 90 100 110 120 130 
PER CENT RATED VOLTS 

d 



FIG. 6-9. Incandescent lamp operating temperatures: (a) 200-watt lamp; (b) 
1,000- and 1,500-watt lamps in PS-52 bulbs; (c) temperature gradient in air surround- 
ings a 100 watt lamp; (d) effect of voltage on temperature. 



6-10 



I E S LIGHTING HANDBOOK 



The following equations enable the lamp user and designer to predeter- 
mine the performance under varying conditions of either gas-filled or vac- 
uum lamps (capital letters represent normal rated values) : 

life '_ / LUMENS y = / LUMENS/WATT \ b = /VOLTSy = / AMPS \" 
LIFE \ lumens / \ lumens/watt / \ volts / \ amps / 



lumens / volts \ k 

LUMENS ~~ \ VOLTS/ 



(ohms y 
OHMS/ 

LUMENS/WATT 

lumens/watt 



amps _ / volts \ * , watts 
AMPS ~ V VOLTS ) WATTS 



/ lumens/watt \ h 

Vlumens/watt/ 



-( 



watts 
WATTS 



\ s _ / amps\ y 
) ~ \AMPS/ 



/ LUMENS y = / VOLTS y = /AMPSy 
\ lumens / \ volts / \ amps / 



/ volts y 

V VOLTS/ 



Table 6-3. Performance Data on Standard Incandescent Lamps 





BULB J 






P 

< 


p 

H 

« 


fa 
13 
w 
o 


z; 

< o 




< 
p< 

w 

Ph 

IS 


pq 

i3w 
< 


w 
Pi 
P 

H 
< 


WATTS 


(Clear 

or 
frosted) 


C/3 

H 
►J 
O 


c/3 

W 
Pi 

W 

s 


02; 


5* 


Pi 2 

W 3 

>S 
<- 

Q 
W 
H 
< 


WO 


Is 

J .2 


H w 

< 


s 

w 

H 

W 

< 






> 

120 


< 


< 


p3 


1,500 


P 
14.4 


E3 


tn 


o 


pq 


6 


S-14 


0.050 


40 


6.6 


0.00047 


3,860 


93 


88 


10 


S-14 


120 


0.083 


80 


8.0 


1,50017.0 


.00065 


3,900 


106 


106 


25 


A-19 


120 


0.21 


260 


10.4 


1,000 


21.9 


.0012 


4,190 


110 


108 


40 


A-19 


120 


0.34 


465 


11.7 


1,000 


15.0 


.0013 


4,490 


260 


221 


60* 


A-19 


120 


0.50 


835 


13.9 


1,000 


20.8 


.0018 


4,530 


252 


195 


100* 


A-21 


120 


0.83 


1,630 


16.3 


750 


22.6 


.0025 


4,670 


261 


201 


100 


A-23 


240 


0.42 


1,240 


12.4 


1,000 


35.7 


.0016 


4.470 


285 


228 


100 


A-23 


30 


3.12 


1,850 


18.5 


1,000 


8.2 


.0062 


4,660 


285 


228 


100 (proj.) 


T-8 


120 


0.83 


1,920 


19.2 


50 


19.4 


.0025 


4,890 


— 


— 


150 


PS-25 


120 


1.25 


2,600 


17.2 


750 


25.0 


.0032 


4,710 


290 


209 


200 


PS-30 


120 


1.67 


3,650 


18.3 


750 


25.2 


.0038 


4,750 


307 


212 


300 


PS-35 


120 


2.50 


5,900 


19.7 


750 


27.6 


.0050 


4,825 


374 


173 


500 


PS-40 


120 


4.17 


10,000 


20.0 


1,000 


31.6 


.0071 


4,840 


389 


213 


1,000 


PS-52 


120 


8.3 


21,500 


21.5 


1,000 


39.5 


.0111 


4,930 


475 


235 


1,000 


PS-52 


240 


4.2 


19,100 


19.1 


1,000 68.3 


.0073 


4,760 


475 


235 


1,000 (proj.) 


T-20 


120 


8.3 


28,000 


28.5 


50 ! 33.4 


.0110 


5,590 


— ■ 


— 


1,000 (spot)f 


G-40 


120 


8.3 


22,500 


22.5 


200 


38.3 


.0114 


5,200 


756 


192 


1,500 


PS-52 


120 


12.5 


33,000 


22.0 


1,000 


43.5 


.014 


5,010 


505 


265 


2,000 


PS-52 


120 


16.7 


44.000 


22.0 


1,000 


46.2 


.018 


5,030 


855 


— 


3,000 


T-32 


32 


93.8 


S8,500 


29.5 


100 


13.6 


.048 


5,390 


— 


— 


5,000 


G-64 


120 


41.7 


164,000 


32.7 


75 


44.4 


.029 


5,360 


860 


— 


10,000 


G-96 


120 


83.4 


325,000 


32.7 


75 54.5 


.046 5,540 


— 


— 



* Coiled-coil filament, f Vertical base down. J See Fig. 6-11. § Under specified laboratory test con- 
ditions. ||The practice is to weigh a length of 20-mm wire and calculate the diameter. If At an ambient 
temperature of 77 degrees Fahrenheit the maximum bare bulb temperature is measured with the lamp 
operating vertically base up; the base temperature is measured at the junction of the base and bulb. (See 
also Fig. 6-9.) 



LIGHT SOURCES 



6-11 



The exponents are as follows: 



Gas-filled lamps 3.86 

Vacuum lamps 3.85 



b 

7.1 
7.0 



d 
13.1 

13.5 



24.1 
23.3 



h 
1.84 
1.82 



Gas-filled lamps 7.36 0.541 

Vacuum lamps 8.36 0.580 



1.54 
1.58 



/ 
0.544 
0.550 



k 
3.38 
3.51 



1.84 
1.93 



2.19 
2.22 



y 
6.25 
6.05 



j 
3.40 
3.33 



Exponents d, k, and t are taken as fundamental. The other exponents are 
derived from them. Values given apply to lamps operated at efficiencies 
near normal and are accurate enough for calculations in the voltage range 
normally encountered. 6 

The curves in Fig. 6-10 show the effects of operating an incandescent 
lamp at other than its rated voltage. These characteristics are averages 
for many lamps of the gas-filled type and are slightly different from those 
of vacuum types. 

180 



2 80 



60 













j 




,t 


V 
















/ 


















/ 


r 
















' /v 


V 


z^z- 














" ,<! 


''/ i 










o£ 


pC^' 




,< 


/' 

W 














<J& 


> S4 
4° / 


/ 












r<fe^ 














■"" 





















40 



40 50 60 70 80 90 100 110 120 130 140 150 
PER CENT RATED VOLTS 

FIG. 6-10. Effect of voltage variation on operating 
characteristics of incandescent lamps. 

Neither the theoretical life of lamps calculated by the exponential rela- 
tionship of life and voltage nor the rated laboratory life is exactly realized 
in practical installations since handling, cleaning, vibration, and under- 
or overvoltage operation introduce factors which are not considered in the 
calculated or laboratory ratings. 

Incandescent Lamp Depreciation and Bulb Blackening 

Multiple lamps depreciate in light output throughout life partly as the 
result of gradual filament evaporation as the lamp is burning; this depre- 
ciation is a normal and inevitable result of operation. As the filament 
evaporates it becomes thinner and its resistance increases and the current, 
wattage, and lumen output all decrease, but not in the same ratio. Figure 
6-2 shows the depreciation in the light output characteristic of a 200-watt, 
general-service lamp. Depreciation curves for other wattage and bulb 
sizes (excepting the silver-processed) will show the same trend. 



6-12 I E S LIGHTING HANDBOOK 

The light output of a series lamp operated at rated constant current 
changes relatively little during life. The filament, evaporating and be- 
coming smaller as the lamp is burned, gradually increases in resistance, 
requiring a rise in voltage to maintain a constant current value. This in 
turn increases the wattage and filament temperature, causing an increase 
both in efficiency and in the lumens produced by the filament. The in- 
creased lumens from the filament may eventually be offset by the light 
that is absorbed as the bulb blackens. The light output of the 15-ampere 
and 20-ampere compensator (series) lamps may drop below the initial value 
early in life and continue to decrease throughout life. Net changes in 
lumen output will vary little with bulb size, shape, and burning position. 

In vacuum lamps the blackening resulting from the tungsten particles 
is spread over the inner bulb surface. In gas-filled lamps the hot gas 
stream carries the particles upward and causes a relatively dark spot to 
appear above the filament. When lamps are burned base up, part of 
the blackening will be deposited on the neck area where much of the light 
is normally intercepted by the base. Thus the lumen maintenance of a 
lamp operated base up will be better than for base-down operation. 

To reduce blackening and to perfect the inner atmosphere, an active 
agent known as a "getter" is used inside the bulb. The chemicals making 
up the getter can be solids applied to the filament or leads or gasses. 

In certain lamps in which blackening would not be reduced enough by 
getters alone, various other means are also employed. Some of the high- 
wattage lamps used in motion picture photography have a small amount 
of loose tungsten powder in the bulb, which, when shaken about, wipes 
off much of the blackening. The general-service, bipost-base lamps have 
a "collector grid" (a wire mesh screen) located above the filament. This 
screen reduces blackening by attracting and condensing the tungsten vapor 
and holding the tungsten particles. 

Lamp Voltage Classes 

Standard general lighting lamp voltages are 115, 120, and 125 volts. 
Lamps generally available in any community should conform to the nom- 
inal voltage of the distribution system serving the territory. Recent 
country-wide surveys of voltages indicated 1.3 per cent of the population 
served at 110 volts, 43.4 per cent at 115 volts, 55.3 per cent at 120 volts, 
and 0.1 per cent at all other voltages in the 110-130 volt range. Lamp 
purchases by voltage do not coincide with these proportions, rather they 
show that a larger proportion of lamps of higher voltage rating are being 
used than service voltages call for. 

High-voltage lamps necessarily have filaments of smaller diameter and 
greater length. The filaments are less rugged, require more supports, 
and are less efficient than those of equal wattage 120-volt lamps. A 240- 
volt lamp will take but half the current of the same wattage 120-volt 
lamp, permitting some economy in the wiring of lighting circuits. 7 



LIGHT SOURCES 6-13 

Low-voltage lamps (6- to 64-volt circuits). Lamps are designed for the 
several classes of low-voltage service generally provided by battery- 
generator systems. For train lighting, lamps are rated 30, 32, 60, and 64 
volts. The 30-volt lamps are also known as "Country Home Lamps" 
because they are used most often in individual farm-lighting systems. 

Battery-generator systems also supply lighting for automobiles, trailers, 
boats, and airplanes, for isolated beacons and aviation landing fields, and 
for many similar places where central station service is usually not avail- 
able. Except that these lamps have conventional large bulbs and bases 
they might be classed as miniature lamps; there is no sharp dividing line 
between the so-called large and miniature lamp classifications. Gener- 
ally speaking, lamps designed for operation on circuits of less than 30 volts 
are considered miniature lamps, and have small bases. 

Low-voltage lamps, because they utilize a shorter and heavier filament 
for a given wattage, are more rugged and, in general, more efficient than 
lamps of the 120-volt class. 8 

Street-railway lamps {525- to 625 -volt circuits). Street-railway service 
requires lamps designed for that application. Circuit voltages (including 
shop and yard circuits) range from 525 to 625 volts. Some lamps are 
designed to operate 5-in-series on these voltages. Dividing the trolley 
voltage by 5 gives the design voltage of the individual lamp. The high 
circuit voltage and the fact that these lamps are connected in series dic- 
tates specially designed lamps for this service. To identify them, lamps 
for street railway service are rated in odd wattages (36, 56, 94, 101, and 
so forth) to distinguish them from multiple burning lamps. The larger, 
gas-filled lamps, identified by the numeral 1 as the last digit, are designed 
and constructed to prevent arcing when burnout occurs. 

The number of 30-volt lamps on a street-railway circuit is determined 
by dividing the trolley voltage by 30. Each lamp is equipped with an 
automatic short-circuiting element which shunts the lamp out of the circuit 
when the lamp burns out. These lamps are rated in amperes instead of 
watts. Lamps rated 1.0 and 1.6 amperes are available. 

Street series lamps. Street series lamps are designed to operate in series 
on constant current circuits. The most common circuit carries 6.6 am- 
peres and is automatically regulated to maintain this current flow regard- 
less of the number of lamps used on the circuit. Lamps are designed also 
for 5.5-, 7.5-, 15-, and 20-ampere operation, the higher currents usually 
being obtained for each lamp by an individual step-up current transformer 
connected to a normal series circuit. These are known as compensator 
lamps. 

Lamps are designated by their rated initial lumen output and ampere 
rating, for example, the 6,000-lumen, 6.6-ampere lamp, or the 25 ; 000-lu- 
men, 20-ampere lamp. Though series lamps as small in output as 250 
lumens are available, the standard sizes range from 1,000 to 25,000 lu- 
mens. Wattage and voltage ratings, as used to designate multiple lamps, 
are not commonly employed. Multiple lamps are designed for a definite 
wattage at a definite voltage and changes in efficiency are shown by 



6-14 I E S LIGHTING HANDBOOK 

changes in lumen output; the lumen output of series lamps, on the other 
hand, remains fixed because generally the lumen output is specified in 
street lighting contracts, and changes in efficiency resulting from improve- 
ments are reflected by changes in wattage or voltage. This usually re- 
sults in odd numbers and fractions, for example, the present 6,000 lumen, 
6.6-ampere lamp has an average rating of 46.9 volts and 310 watts. 

On a constant current circuit the filaments for all sizes of lamps of a 
given current rating are of approximately the same diameter but vary in 
length according to the lumen output. The lamp voltage will vary with 
the lumen output, ranging from a few volts in the smaller sizes to 50 or 
60 volts for the lamps of high lumen rating. 

Series circuits should be closely regulated as fluctuations from normal 
current will cause considerable variation in lamp performance. The 
effect of current variation in series operation is considerably greater than 
that of voltage variation on multiple operation. Roughly a 1 per cent 
change in amperes (0.066 ampere on a 6.6-ampere circuit) will produce 
a change of about If per cent in volts, about 2f per cent change in watts, 
about 3| per cent change in efficiency, about 7 per cent change in light 
output and about 20 per cent change in life. 

The increase in voltage and wattage of lamps on series circuits will 
amount to about 4 per cent above the initial rating at the end of their 
rated life, averaging about 2 per cent during life. Provision should be 
made in the capacity of constant current transformers for this increase in 
voltage. 

Bulb Shapes and Finishes 

Shapes of common incandescent lamp bulbs are shown in Fig. 6-11. 
_For general lighting there is almost complete standardization of lamps in 
the A and PS bulb shapes. Lamps rated 15-100 watts are frosted inside. 
Lamps in the 150-1,500 watt range may be either clear or frosted. Flame- 
shaped and round-bulb lamps are available in 15-, 25-, and 40-watt sizes 
for ornamental fixtures where the bulbs are exposed and where the bulb 
shape is related to the artistic design of the luminaire. 

Tubular bulb lamps extend lighting applications since they can be 
placed in small inconspicuous reflectors for display cases, small coves, and 
narrow cavities. Intermediate and medium screw bases are used on these 
sources. Projection lamps employ tubular bulbs because of space limi- 
tations; prefocused bases are most common. The Lumiline lamp repre- 
sents a considerable departure from conventional lamp construction since 
the filament extends between the contact caps at the ends. Special disk 
bases and lamp holders are employed. The lumen output of tubular 
bulb lamps is reduced below that of globe-shaped lamps of the same wattage 
rating because the additional supports required cause a heat loss. 

Many types of lamps are available with bulbs made of "hard" or "heat- 
resisting" glass. Such bulbs withstand higher temperatures than ordinary 
lead or lime glass, and are used on most lamps of the spotlight, flood- 



LIGHT SOURCES 



6-15 




FIG. 6-11. Shapes of common incandescent lamp bulbs. In bulb-type designa- 
tions the letters indicate shape; numerals following the letters indicate the 
nominal diameter in eighths of an inch. 

light, and projection types and for general applications where high-wattage 
lamps are exposed to rain or snow. 

( Bulb finishes and colors. Inside frosting is widely applied to many 
types and sizes of bulbs. Frosting gives moderate diffusion of the light, 
thus reducing the extremely high filament brightness when lamps are 
used exposed, and eliminating striations and shadows when used in most 
types of equipment. By frosting inside the bulb, the outer bulb surface 
is left smooth and easily cleaned; furthermore, the light absorbed by the 
inside frosting is scarcely measurable. Though white glass or white-coated 
bulbs give greater diffusion, the loss of light is of the order of 15 per cent. 

White bowl lamps have a white diffusing coating on the inside of the 
bowl and are applicable principally in open direct-lighting reflectors. 
This coating redirects about 80 per cent of the incident light upward, 20 
per cent being transmitted diffusely through the bowl. Thus the bulb 
brightness of these lamps is considerably lower than that of the clear bulb 
type of the same wattage. 

J)aylight lamps have blue-green glass bulbs which absorb some of the red 
ancTyellow wavelengths.. They therefore have a higher color temperature 
and appear whiter. The color correction accomplished at the expense of 
about 35 per cent reduction in light output through absorption falls about 
midway between unmodified tungsten-filament light and standard natural 



6-16 I E S LIGHTING HANDBOOK 

daylight. The color temperature of daylight lamps varies between 3,500 
to.4,000 degrees Kelvin. 9 

Colored lamps in diffusing bulbs are available in three different types cf 
finishes: (1) outside spray-coated, (2) inside-coated or enameled, and (3)~ 
ceramic glazed glass. Outside-coated lamps are suitable for indoor use 
where not exposed to the weather. Their surfaces collect dirt readily 
and are not easily cleaned,. Inside-coated or enameled bulbs have smooth 
outside surfaces that are easily cleaned. The pigments are not subjected 
to weather and therefore have the advantage in permanence of color. 
Ceramic glazed finish is a recent development which gives a permanent 
finish to the bulb with the ceramic pigments fused into the glass but some 
colors are not as uniform and the efficiency attainable is approximately 
20 per cent lower than equivalent lamps of clear or natural-colored glass. 

Natural-colored-glass lamps are used where permanence of color is desired. 
These lamps cost somewhat more than coated lamps but because of their 
greater efficiency of light transmission, the over-all cost of producing 
colored light with natural colored lamps is about the same as with coated 
lamps. Only a few colors (ruby, blue, green, and amber) are regularly 
available. 

Reflector-Type Lamps 

This general designation refers to lamps in which light control is built 
into the lamp itself by applying either silver or aluminum to the out- 
side or the inside surface of the bulb. Not only has a reflecting surface 
been applied to common bulb shapes but also quite a number of bulbs have 
been developed in which bulb contour and reflecting surfaces are co- 
ordinated to provide specific distributions of light. The most extensive 
use of specialized bulb contours has been in the sealed beam headlamps 
found in 1940 and later automobiles. 

Silver ed-bowl lamp. The silvered bowl lamp represents the most com- 
mon reflector lamp for general lighting applications. Such lamps are 
processed in two ways, with silvering applied either internally or externally. 
In the latter type of lamp a finish of pure silver is deposited on the bulb 
and sealed with an electrolytic coating of copper; over these two metal- 
lic coatings an aluminum or bronze finish is applied. The reflecting sur- 
face is thus protected from all dust, dirt, and deterioration. . The light 
control achieved is accompanied by an initial loss of only 6 to 10 per cent 
in light output. 

This process has also been applied in neck silvering, and such lamps are 
being used to provide the specialized light distribution required for street 
lighting service, or for such general applications as high-bay and window 
lighting. 10 

Projector lamp. A wide variety of light beam patterns can be incor- 
porated in a lamp by co-ordinating filament positioning with respect to 
special bulb reflecting contours. In the projector flood and projector 
spot lamps, designated as type PAR, the bulb is constructed of two molded 
glass sections. A bowl-shaped section of parabolic or other suitable con- 



LIGHT SOURCES 



6-17 



PROJECTOR LAMP PAR- 



tour on which a highly efficient reflector lamp r- 4 o 

reflecting film of aluminum has 
been vaporized serves as the 
reflector. This section incor- 
porates the base and filament. 
A molded glass cover plate, 
either clear or configurated in 
any desirable lens pattern, is 
then fused to the reflector sec- 
tion. Made of hard glass, this 
type of lamp may be used out 
of doors without danger of ther- 
mal cracks. Louvers, shields, 
and color filter fittings may be 
supported by the bulb. 

Reflector lamp. The reflec- 
tor lamp has a blown glass 
bulb of special reflector contour 
and an inside aluminized or 
stive red surface. This con- 
^struction is less expensive than 
type PAR, used in projector 
lamps. It is suitable for in- 
terior spotlighting and flood- 
lighting but the practice of 
spring fitting accessory shields 
and filters to these bulbs is not 
advisable because of the likeli- 
hood of thermal cracks and 
premature lamp failure. 

Candlepower distribution 
curves for various sizes of pro- 
jector and reflector lamps are 
shown in Fig. G-12. 

Type L (sealed-beam) reflector lamps. In the sealed-beam headlight 
systems, fog lamps, spot lamps, tractor lamps, airplane landing lamps, 
signaling lamps, and so forth, one or two filaments are accurately mounted 
with respect to an aluminized glass reflector and this is then hermetically 
sealed to the cover lens. The lamp is gas-filled, the sealing tube sealed 
off, and the lamp based with special prong or screw terminals. Three 
advantages of this construction are: 

~~T. The glass reflector section is of reasonably precise contour and is not 
subject to denting or springing out of shape during processing and hand- 
ling. This results in good beam control. 11 

2. The short stocky filament supports are rugged and filaments are 
carefully positioned before the lens section is sealed on. 

3. Aluminum vaporized on glass is one of the best reflectors, does not 
tarnish, and as a sealed-in reflecting surface is not subject to the deprecia- 




ISO-WATT FLOODLIGHT 

300-WATT FLOODLIGHT 

150-WATT SPOTLIGHT 

' 300-WATT SPOTLIGHT 



FIG. 6-12. Candlepower distribution char- 
acteristics of several reflector lamps. 



6-18 I E S LIGHTING HANDBOOK 

tion from dust, dirt, and moisture, which succeed by "breathing action" 
in getting into all except the most perfectly gasket ed enclosures. 

Photographic and Projection Lamps 

Photoflood, photoflash, and phoio-enlarger lamps as well as projection and 
photocell exciter types are described in Section 14. 12, 13, 14 ' 15 

Other Incandescent Lamps for Specialized Service 

Lamps made in very small quantities for specific applications are some- 
times available even though not found in the standard lamps catalogues. 
Unless a very large number of lamps (more than 20,000, for instance) is 
desired, it is usually not feasible to develop a new design. 

Spotlight and floodlight lamps. Lamps for this service have concentrated 
filaments, u'sually of type C-5, accurately positioned with respect to the 
base. When the filament is placed at the focal point of a reflector or lens 
system, a sharply controlled beam is obtained. 

Photometric standard lamps. These lamps of both the vacuum and gas- 
filled type are available for use with comparison photometers, and are 
specially made to ensure stability and uniform performance. 16 

Bake-oven lamps. These sources have four special features not included 
in low-wattage, general-service lamps: (1) a special basing cement which 
will withstand temperatures up to 550 degrees Fahrenheit is used; (2) 
the lead wires are welded to the base; (3) an asbestos insulation is placed 
between the leads in the base so that falling oxide will not cause a short 
circuit; and (4) bake-oven lamps undergo a special high-temperature ex- 
haust, giving improved operation and longer life at the high external tem- 
perature involved. 

Rough-service lamps. The filaments (C-17 or C-22) of lamps designed 
to withstand shocks and bumps are coiled on a very small mandrel. This 
results in a relatively long coil which is carefully mounted and held by 
many supports (the 50-watt, 115-volt, rough-service lamp has sixteen 
supports). Because of the number of supports, the heat loss is higher and 
the efficiency lower. These lamps find their principal application in port- 
able luminaires on extension cords in garages, industrial plants, and similar 
places. (See Fig. G-5b.) 

Vibration-service lamps. Most lamps have coiled filaments made of a 
specially prepared tungsten having high sag resistance. However, those 
vibration lamps designed for use where continuous high-frequenc}^ vibra- 
tions would cause early failure of general-service lamps, are made with a 
more flexible tungsten filament. The sagging characteristic of the wire 
used allows the coils to open up under vibration, thus preventing short 
circuits between coils. 

Vibration and shock frequently accompany each other and sometimes 
only experiment will determine the best lamp for the purpose. Vibration- 
resisting adaptor socket mounts utilizing a coiled spring or other flexible 
material to deaden vibration have been employed where general-service 
lamps are used under conditions of severe vibration. 17 (See Fig. 6-5c.) 



LIGHT SOURCES 



6-19 



Miniature lamps. See Section 15. 

Lumiline and showcase lamps. The Lumiline type has two disk bases, 
one at each end of the lamp, with the filament connected between them. 
The filament, in the form of a loose coil, is supported at intervals along the 
tube from a small metal channel next to the inside wall of the tube and 
insulated from the two contact ends. Thirty and 60- watt sizes are avail- 
able in the 18-inch length, and the 40-watt is made in a 12-inch length. 
All sizes are available in either clear or inside-frosted tubes, or in various 
color coatings. 

Showcase lamps have a conventional screw base. The longer lamps 
have elongated filaments with filament supports similar to Lumiline lamps. 
The common sizes are 25 and 40 watts, but sizes up to 150 watts are 
available. 

Three-light lamps. These employ two filaments, operated separately 
or in multiple to provide three levels of illumination. The common fila- 
ment lead-in wire is connected to the shell of the base; the other end of 
one filament is connected to a ring contact and the end of the other fila- 
ment to a center contact. 

Sign lamps. While large numbers of gas-filled lamps are used in en- 
closed and other types of electric signs, those designated particularly as 
"sign" lamps are mostly of the vacuum type. Lamps of this type are 
best adapted for exposed sign and festoon service because the lower bulb 
temperature of vacuum lamps minimizes thermal cracks resulting from 
rain and snow. Some low-wattage lamps, however, are gas-filled for use 
in flashing signs. Bulb temperatures of these low- wattage, gas-filled lamps 
are sufficiently low to permit exposed outdoor use. See Fig. 6-8. 

Incandescent Lamp Bases 

Types and dimensions of bases used on common incandescent lamps 
have been standardized rather completely. Figure 6-13 shows the com- 
mon types of incandescent lamp bases. 







a u 



MINIA- CANDE- INTER- MEDIUM 

TURE LABRA MEDIATE 



SKIRTED MINIATURE MINIATURE 
BAYONET FLANGED 







III 


III 


II III 




fa^^l 









BAYONET BAYONET DISC 

CANDELABRA CANDELABRA 
PRE FOCUS- 
ING COLLAR 



MEDIUM MOGUL 

PREFOCUS PREFOCUS 




FIG. 6-13. Common incandescent lamp bases. 



6-20 



I E S LIGHTING HANDBOOK 



50 
0.38 



I 


POSITIVE CRATER RADIATION ONLY 
13.6 MM SUPER HIGH INTENSITY POSITIVE 
7/[ 6 -INCH EXTRA HEAVY COPFER 
COATED NEGATIVE 


1 


















d 






a 
































b 























0.70 



0.45 0.50 0.55 0.60 0.65 
WAVELENGTH IN MICRONS 
1 micron = 10,000 angstroms = 1/10,000 centimeter 

FIG. 6-14. Spectral distribution of radiant 
energy at a distance of 10 feet from a direct- 
current arc (high-intensity, motion-picture- 
projector carbons) operated at (a) 185 amperes, 
75 volts; (b) 140 amperes, 60 volts. 



CARBON -ARC LAMPS 

Arc sources, which were the first commercial^ practical electric light 
sources, now are used where an extremely high brightness "point" source 
is necessary, or where their radiant energy spectrum is advantageous. 

Figure 6-14 shows the spectral 
energy distribution from a 
high-intensity, direct-current 
arc (motion picture projector 
carbons). Arcs may be oper- 
ated either in the open air or 
within a glass or quartz en- 
closure. 

Because of the negative volt- 
ampere characteristic of arcs, 
they must be operated on cir- 
cuits including ballast resis- 
tances or reactances (either in 
the generating or rectifying 
equipment or as separate units 
in the arc circuit). In starting 
a carbon arc it is necessary to 
bring the two electrodes to- 
gether instantaneously, after 
which they are separated to 
the proper distance to main- 
tain the correct arc voltage and current. These conditions can be main- 
tained and the carbon fed manually, but in most carbon arc lamps 
automatic mechanisms feed the carbons as they are consumed, and regulate 
the arc length and position of the light source. 13 ' 19 

The source of light in a carbon arc is the incandescent solid crater in the 
plain- or low-intensity arc, the incandescent vapors of the cerium rare- 
earths in the cup-shaped crater of the high-intensity arc, and the arc 
stream or "flame" in the flame arc, as shown in Fig. 1-10, page 1-15. 
Table 6-4 gives the color characteristics of various arcs in reference to 
average daylight and to sunlight. See Section 14 for applications. 

ELECTRIC DISCHARGE LAMPS FOR LIGHTING APPLICATIONS 

Mercury, sodium, and neon are the elements most widely used at pres- 
ent in discharge lamps because the temperature, pressure, voltage, and 
other related considerations necessary to produce light utilizing these ele- 
ments are relatively easy and inexpensive to provide. Different metals 
may be used for electrodes. These are often coated with electron-emis- 
sive barium or strontium oxide. Electrodes emit electrons more readily 
when hot than when cold.' 20 

Once started, discharge lamps may operate at less than line voltage; 
the heating effect of the arc keeps the electrodes hot regardless of starting 
temperature. The enclosed arc emits light at the instant when the dis- 
charge begins between one electrode acting as a cathode and the other 
acting as an anode. If connected to an alternating-current power supply, 
the electrodes exchange functions as the power supply changes polarity. 



LIGHT SOURCES 



6-21 



Table 6-4. Color Temperature of Carbon Arcs with Dominant Wave- 
length and Per Cent Purity Referred to Average Daylight (6,500 degrees 
Kelvin) and to Noon Sunlight (4,200 degrees Kelvin) at Springfield 

Lake, Ohio 19 



LIGHT SOURCE 



11-mm high-intensity carbons. 

8-mm Suprex carbons 

8-mm Suprex carbons 

16-mm high-intensity carbons. . 

7-mm Suprex carbons 

§-inch x 12-inch rotary spot car 

bons 

6-mm Suprex carbons 

9-mm high-intensity carbons . . 

7-mm Suprex carbons 

13. 6-mm super-high-intensity 

carbons 

13 . 6-mm high-intensity carbons 

6-mm Suprex carbons 

8-mm motion-picture-studio 

carbons 

12-mm low-intensity carbons. . 



AM- 
PERES 



90 
65 
56 
150 
50 

80 
40 
70 
42 

185 

125 

30 

40 
30 



VOLTS 


COLOR 
TEM- 
PERA- 
TURE 

(K) 


56.5 
38.0 


6,400 
6,400 


43.0 
81.0 


6,250 
6,000 


36.0 


5,950 


53.0 


5,600 


32.0 
49.0 


5,850 
5,800 


33.0 


5,800 


75.0 


5,480 


63.0 


5,650 


28.0 


5,250 


37.5 


4,650 


55.0 


3,550 



DOMINANT 
WAVELENGTH 

(MICRONS) 
REFERRED TO 



Daylight Sunlight 



0.5640 
.5650 
.5700 
.5740 
.5710 

.5900 
.5750 
.5760 
.5740 

.5740 
.5730 
.5770 

.5780 
.5830 



0.4800 
.4800 
.4790 
.4780 
.4800 

.4750 
.4790 
.4780 
.4790 

.4800 
.4800 
.4780 

.4750 
.6050 



PURITY 

(PER CENT) 

REFERRED 

TO 



Day- 
light 



4 

5 
5 
7 
9 

9 
9 

9 
10 

10 
12 
16 

25 
40 



Sun- 
light 



22 
21 
20 
18 
19 

17 
18 
17 

17 

14 
16 
13 

6 

9 



Because discharge lamps, like other arc sources, have an inherent nega- 
tive resistance characteristic, suitable current ballast or control as well as 
starting equipment is necessary. 

This current-limiting equipment (sometimes referred to as the "auxil- 
iary") is necessary for the operation of every discharge lamp. It increases 
the total power consumed and, if not "power factor corrected," reduces 
the power factor of the circuit below that of the lamps. Power factor cor- 
rection by capacitors is effective and frequently practiced. 21 

Mercury- Vapor Discharge Lamps 

The mercury-vapor pressure at which a lamp operates accounts in a 
large measure for its characteristic spectral energy distribution. In gen- 
eral, higher operating pressure tends to shift a larger proportion of the 
emitted radiation into longer wavelengths. At extremely high pressures 
there is a tendency to spread the line spectrum into wider bands. Within 
the visible region the mercury spectrum consists of four principal wave- 
lengths which result in a greenish-blue light at efficiencies of 30 to 65 
lumens per watt. While the light source itself appears to be a bluish white, 
there is an absence of red radiation in the low- and medium-pressure lamps 
and most colored objects appear distorted in color value. Blue, green, 
and yellow colors in objects are emphasized; orange and red appear 
brownish or black. For this reason and because several minutes may be 
required for restarting after a momentary interruption in current, mercury 
lamps are often combined with incandescent lamps in installations where 
it is desired to approximate average daylight conditions. 22 A summary 



6-22 



I E S LIGHTING HANDBOOK 



T V 



j£f^^ 




MOGUL 
SCREW BASE 



7-f IN. 



STARTING 
RESISTOR 



METAL . 
SUPPORT 



13 IN 



CENTER 



METAL 
SUPPORT 




STARTING 
T" ELECTRODE 
UPPER MAIN 
ELECTRODE 



of existing technical data on the common types of mercury-vapor lamps is 
given in Table 6-5. 

Types A-Hl and B-Hl . The 400- 
watt, type A-Hl lamp is the most 
widely used of all mercury lamps, 
and is employed frequently in factory 
lighting, exterior floodlighting, and 
street lighting. As shown in Fig. 
6-15, two main electrodes are located 
at opposite ends of the 7f -inch glass 
tube in which the mercury that 
maintains the arc is vaporized. 
These electrodes are of coiled tungs- 
ten wire, covered with a barium- 
strontium oxide. 

The arc tube contains a small 
amount of pure argon gas which is 
supporting used as a conducting medium to fa- 
cilitate the starting of the arc before 
the mercury is vaporized. Near the 
upper end of the tube is a starting 
electrode which is connected elec- 
trically to the lower electrode through 
a resistor. When current is applied, 
an electric field is set up between the 
starting electrode and the upper main 
electrode, causing an emission of 
electrons from the active surface of 
the main electrode. This imparts 
energy to the gas in the arc tube so 
that it becomes conducting. 

The quantity of mercury in the 
FIG. 6-15. Type A-Hl, 400-watt, mercury arc tube is measured so as to main- 
-vapor lamp. tain a vapor pressure approximately 

equal to one atmosphere. 
The 400-watt arc tube is enclosed in a larger tubular bulb which reduces 
the effect of ambient temperature. About half an atmosphere of nitrogen 
is introduced in the space between the arc tube and the outer bulb. 

Type A-Hl is for base-up operation. Type B-Hl is for base-down 
operation. The chief difference is in the relative position of arc tube 
sealing-tip and base. In both types the arc tube is mounted so that the 
sealing tip is at the top in order that none of the mercury will be pocketed, 
which might interfere with its complete vaporization, reduce the mercury- 
vapor pressure below normal, and result in lower efficiency. Both t}^pes 
must be operated in a vertical position in order to keep the arc stream in 
the center of the tube. If the lamp axis is deviated from vertical more 
than 10 degrees, the arc stream will bow until it touches the side of the 
tube, at which point it will quickly melt the glass and ruin the lamp. 




T-ARC TUBE 



-OUTER TUBE 



LOWER MAIN 
' ELECTRODE 



LIGHT SOURCES 



6-23 



Table 6-5. 



Characteristics of Several Mercury- Vapor-Discharge Lamps 
Used in General Lighting 



DESIGNATION* — » 


A-Hl 
B-Hl 
F-Hl 


A-H4 


C-H5 


A-H6H 


A-H9 


E-Hl 


A-H12 




400 

452 

440/lamp 


100 
120 


250 

290 

286/Iamp 


1,000 
1,095 


3,000 
3,220 


400 
450 


1,000 


Watts, with single-lamp 
transformer 

Watts, with two-lamp 
transformer 




Lumens at 100 hours 

Lumens (approx. initial) . . . 
Lamp lumens per watt at 

100 hours 

Over-all lpw (single-lamp 

transformer) 


16,000 
16,000 

40 

35.4 


3,000 
3,000 

30 

24.4 


10,000 
10,000 

40 

34.5 


65,000 

65** 
59.4 


120,000 
120,000 

40 

37.3 


20,000 
20, 000 

50 

44.2 


60,000 
60,000 

60 


Rated average life (hours) . . 

5 hours per start 

10 hours per start. 


4,000 
6,000 


1,000 


2,000 
3,000 


75 


3,000 


2,000 
3,000 


2,000 


Outer bulb size 


T-16 

Clear 

Mogul|| 

t 


T-10 

Clear 

Admed. 

Any 


T-14 
Clear 
Mogul 

Any 


T-2 

Clear 
Ts-in. 
sleeve 

Horiz. 


T-9h 

Clear 

S-c term. 

Any 


T-20 

Clear 

Mogul 

screw 

Any 


T-28 
Clear 


Base type 

Burning position 


Mogul 

screw 

mech. 

Any 


Max. over -all length (inches).. 
Light center length (inches) 
Vapor pressure (atmospheres) 
Number of electrodes 


13 
7| 
1.2 

3 

6 
Glass 


5| 

8 

3 

1 

Quartz 


8 
5 
4-4.5 
3 
If 
Quartz 


3i 

110 

2 

1 

Quartz ft 


54f 

0.55 
2 

48 
Glassft 


11 

7 

2.5 

3 

2f 
Quartz 


14 
9 
1.5 
3 
5 






Supply voltage (primary 
volts)t 

Lamp-operating volts 

Transformer secondary open 
circuit voltage 

Lamp-starting current (am- 


115,230 
136 

220 

4.7 

3.2 


115, 230 
130 

247 

1.3 

0.9 


115, 230 
135 

250 

2.9 

2.1 


115,230 
840 

1,200 

2.5 

1.4 


230, 460, 575 
535 

850 

9.3 

6.1 


115 
135 

220tt 

4.7 

3.2 


115 
135 

220» 

12 


Lamp-operating current (am 


8.2 






Power factor (per cent on lag 


60, 90, 95 
7 min 
7 min 


50,90 
3 min 
3 min 


50, 90, 95 
4 min 
4 min 


3 sec 
2 sec 


90 

7 min 

8 min 


4 min 
4 min 




Starting time to full output . . 


4 min 







(Examples A-H4, B-H4, C-H4, and S-4 all 

These 



* The suffix number indicates the transformer required, 
operate on an H4 transformer). 

f Burning position. A-Hl and F-II1 are for base-up burning, B-II1 is for base-down burning. 
types must be operated within 10 degrees of vertical. 

X Supply voltage. Transformer design is centered for the range of standard voltage circuits. 

§ Power factor. The higher power factor is obtained with transformers incorporating integral correc- 
tion. Transformers for operating two lamps of types A-Hl, B-Hl, A-H5, and C-H5 have an over -all power 
factor of 95 per cent. 

|| The F-Hl lamp is designed for street-lighting service and, except for a mechanical-type base, it has 
the same characteristics as the A-Hl. 

f A-H6 is water-cooled and requires a water jacket of quartz or heat-resisting glass. B-H6 is air-cooled 
and rated at 900 watts. Its characteristics are similar to the A-H6. 

** Initial lumens per watt (life less than 100 hours). 

ft Single bulb lamp; the outer bulb is the arc tube. 

XX For normal indoor use. Higher open circuit voltages are desirable for dependable starting at lower 
temperatures. 



The starting characteristics of type A-Hl are shown in Fig. 0-16. When 
the current flow r s the argon arc is seen for a few r seconds as a bluish glow 
that fills the entire arc tube. The voltage rapidly increases until the 
lamp reaches a stable operating condition. This takes place in about 7 
minutes, at which time all of the mercury is completely vaporized and the 
lamp operates at about 136 volts, 3.2 amperes. At this stage the arc no 



6-24 



I E S LIGHTING HANDBOOK 



< 2 



O 
h > IOO 



50 











LAMP WATTS 










LAMP 


vm TS 




















/ 




\L_AMP AMPERES 








V_^ 


y 

















1 1 
/-^LINE WATTS 






















■ — -/ 


^-^ 








s , 
















■^1 INE AMPERES^ 








TRANSFORMER 
<L LOSSES 






| 



500 



10 12 2 

TIME IN MINUTES 



FIG. 6-16. Starting characteristics of type A-Hl, 400-watt, mercury-vapor lamps. 



longer fills the tube but is concentrated in a pencil-like arc stream of high 
brightness centered in the inner bulb. At full brightness the lamp produces 
approximately 16,000 lumens. 

If the current is interrupted while the lamp is in operation, the lamp 
cannot be relighted for about 7 minutes. In this time it will cool enough 
to reduce the mercury-vapor pressure sufficiently to allow the arc to strike 
again. If the circuit is not broken this will occur automatically. 

Type A-Hl lamps must be operated within rather close voltage limits, 
and transformer taps are provided for satisfactory operation over a wide 
range of line voltages. For best performance mercury- vapor lamps 
should not be operated from line voltages more than 5 per cent above or 
more than 2| per cent below the rated tap voltage of the transformer 
involved. The effects of voltage on operating characteristics of type 
A-Hl lamps are shown in Fig. 6-17. 

Type E-Hl . This type has an inner quartz bulb for applications requiring 
operation in a horizontal position or at an angle larger than 10 degrees 
from the vertical. The lamp produces 20,000 lumens. 

Type Hj. The 100-watt, type A-H4 lamp shown in Fig. 6-18 is some- 
times referred to as a "capillary" lamp because the arc discharge takes 
place within a small capsule-like tube of quartz. This construction with 
short arc length and small diameter allows operation at high vapor pres- 
sures and temperatures. The outer bulb serves merely as a protective 
container and can be of any convenient size or shape. 

Type H4 comes up to full brightness in from 2 to 3 minutes, starting 
with a blue (argon) glow and gradually assuming its normal operating 
color and efficiency. The arc will be extinguished in event of current in- 
terruption but will restart automatically after a cooling period of 2 to 3 
minutes. These lamps will remain in operation even with a 20 per cent 
decrease from normal operating voltage, showing, in this respect, con- 
siderably more stability than the type A-Hl lamp. However, they will not 
start at such a low voltage. 23 

Type H5. The type H5 mercury-vapor lamp is a 250-watt capillary 
source similar in construction to type H4 but with longer bulbs and bases. 



LIGHT SOURCES 



6-25 



150 
140 
130 

120 
110 
?. 100 



UJ 



w 



\ 













/ 


/ 












/ 


// 










/ 


/ 


7 










{/ 


r 








ZZ** 


;/ 


r 






^^ 












*® 


& 










<t<* 


Y 


'/ 










ifiy 












v/ 





























T~T 



SUPPORTING 
LEADS 



_j LI GHT 

CENTER 

TUBE-SUPPORTING ^\ 
CUPS 



as 90 95 100 105 IIC 115 
PRIMARY VOLTAGE IN PER CENT 
OF TRANSFORMER TAP SETTING 



Jfc 



ADMEDIUM 
SCREW BASE 

-STARTING 
RESISTOR 

STARTING 
ELECTRODE 

MAIN 
ELECTRODES: 

— UPPER 

— LOWER 

-ARC TUBE 
■t-OUTERTUBE 



FIG. 



6-18. Type A-H4, 
vapor lamp. 



mercury - 



FIG. 6-17. Effect of voltage on 
the operating characteristics of type 
A -HI, 400-watt, mercury-vapor 
lamps. 

Type H5 produces 40 lumens per watt. The type C-H5 lamp has been 
employed to some extent for outdoor floodlighting and highway tunnel 
lighting. 

Type H6. The 1,000-watt, type A-H6 mercury lamp consists of a 
capillary quartz tube about If inches long, having an outside diameter of 
I inch and a bore of A inch. Sealed into each end is a tungsten wire 
which serves both as electrode and lead. The tips of these wires project 
just through the surface of a small mercury pool in each end of the lamp. 
The pressure in the capillary when the lamp is not operating is about one 
fifteenth of an atmosphere, the pressure of the argon gas with which the 
lamp is filled. The lamp reaches its full brightness in 1 or 2 seconds after 
power is applied, the heat from the arc quickly vaporizing the mercury 
and building up the pressure to about 110 atmospheres (1,620 pounds per 
square inch). 24 

Because of the high wattage concentrated in such a small volume, in 
order to maintain reasonable operating temperature it is necessary that 
water be passed over the capillary tube fast enough to prevent the forma- 
tion of steam bubbles on its quartz surface. To accomplish this, a "ve- 
locity tube" is placed around the lamp with a very small radial clearance 
through which the water must flow. Because the cross section of the 
water path is so restricted, sufficient velocity to prevent steam formation 
is attained with a water flow of about 3 quarts per minute. More than 
90 per cent of the infrared radiation is absorbed by the circulating water. 

The lamp produces 65,000 lumens with a maximum surface brightness 
of 195,000 candles per square inch (one fifth the brightness of the sun). 
Because heat storage is small and cooling rapid, type H6 lamps may be 
restarted at once after the current has been turned off. During life, the 
lamp voltage gradually increases and the current and the wattage decrease. 



6-26 



I E S LIGHTING HANDBOOK 



The life depends on the number of times the lamp is started and the type 
of service. There may be more variation in the life of individual lamps of 
type H6 than in the life of lamps of other types. 

Type 119. The 3,000-watt, type A-H9 mercury lamp is a tubular source 
about Iys inches in diameter and 54f inches in length over all. The light 
source length is about 48 inches. The lamp has a porcelain base at either 
end with single-contact terminals. The rated life is 3,000 hours, based 
on 5 hours operation per start. Its initial light output rating (after 100 
hours operation) is approximately 120,000 lumens. 

Type A-H9 requires about 7 minutes to reach full light output under 
normal conditions. If the current is interrupted or drops sufficiently to 
extinguish the arc, about 8 minutes cooling will be required before the arc 
will restrike. 

Mercury-vapor-discharge lamp auxiliary equipment. Ballast for type 
Hi, H4, H5, and H6 lamps is provided in the form of step-up autotrans- 
formers with voltages sufficiently high to establish the arc without exter- 
nal starting mechanisms. Magnetic shunts or separate reactors are used 
as a means of regulating the lamp currents. Power factor correction is 
obtained by primary capacitors in the case of single lamp units and, 
where two lamps are operated from a single ballast, by phased circuits. 
Figure 6-19 shows typical circuits. 





FIG. 6-19. Typical circuits for operating mercury vapor lamps: (a) single-lamp 
circuit; (b) two-lamp circuit. 

Transformers for the type A-H9 lamp are made for 115-, 230-, 460-, and 
575-volt circuits. All have taps for 95, 100, and 105 per cent of rated line 
volts and include a built-in capacitor for power factor correction. 
The autotransformer and connection leads are carried into a wiring com- 
partment for direct conduit connection of line and lamp. The total 
power consumed by lamp and transformer is about 3,220 watts for the 
230-volt transformer. 21 

Sodium- Vapor Discharge Lamps 

Electric discharge lamps using sodium vapor possess inherent possibili- 
ties for high luminous efficiency because the wavelength of the monochro- 
matic yellow radiation from such a discharge is very close to that of maxi- 
mum luminosity in the spectrum. Efficiencies of 100 lumens per watt 
have been obtained with experimental sodimn lamps and 50 lumens per 
watt is secured in practice. The two sodium lamps in commercial use 



LIGHT SOURCES 



6-27 



T 



12 IN. 



-BASE CONTACTS 



- TUBE BASE 
(SOCKET NOT 
SHOWN) 




at present are the 180-watt, 10,000-lumen lamp and the 145-watt, 6,000- 
lumen lamp. These are applied principally to street and highway light- 
ing and can be used on either series or multiple circuits. 25 

The 10,000-lumen lamp shown in Fig. 6-20 consists of a tubular inner 
bulb about 12 inches long and about 3 inches in diameter placed within a 
double-walled vacuum flask to maintain the proper temperature. The 
inner bulb contains a small quantity 
of sodium, and some neon gas to 
facilitate starting. Coiled filaments 
at either end serve as cathodes with 
one side of each filament connected 
to molybdenum anodes. Four base 
contacts are required. This lamp 
has an average life of 3,000 hours 
under normal street or highway light- 
ing service. It has a starting volt- 
age of 50, a normal operating voltage 
of 30, and a current rating of 6.6 am- 
peres. 

On closing the lamp circuit to begin 
the starting operation a time-delay 
relay allows the cathodes to heat. 
Then the circuit is broken and the 
induced voltage of the transformer 
starts a discharge of a characteristic 
red color through the neon. As the 
temperature rises the sodium evapo- 
rates and gradually the sodium vapor 
discharge comes up to its full bright- 
ness and normal yellow color. This 
warm-up requires about 30 minutes. 

The auxiliary equipment for street FIG - 6 " 20 - 10,000-lumen, sodium-vapor 
series operation of the 10,000-lumen amp ' 

sodium lamp consists of a time-delay switch arrangement for preheating 
the cathodes and a radio interference suppressor. For operation on 
multiple circuits a reactive ballast must also be provided since the multiple 
circuit does not regulate the current. 

A sodium lamp for laboratory work is also available. The total input 
is 60 watts and the lamp itself consumes 28 watts. The high-resistance 
ballast used with this lamp results in some sacrifice in efficiency but en- 
sures the stability of operation necessary for laboratory measurements. 

Miscellaneous Electric Discharge Lamps 

Glow lamps. These lamps, which may have a rating as low as 0.3 lu- 
men per watt, are impractical sources for general illumination, but they 
are often used as signal, pilot, or night lights. The typical lamps shown in 




DOUBLE-WALLED 
t~ EVACUATED 
FLASK 



CATHODE 
"(FILAMENT) 



6-28 



I E S LIGHTING HANDBOOK 



Fig. 6-21 emit light having the spectral character of the inert gas with 
which they are filled. The glow occurs around the negative electrode 
where free electrons strike atoms of the gas and cause them to radiate. 26 





NE-2 NE-51 NE-26 NE-48 NE-27 NE-30 NE-34 

FIG. 6-21. Typical glow lamps. 



FIG. 6-22. Type 
CR-1 crater lamp. 



Glow lamps will operate on alternating-current or direct-current circuits 
at voltages as low as 70. Like other discharge lamps, glow lamps re- 
quire a limiting resistance in series. In screw-base lamps this resistor is 
incorporated in the base or in the bulb; in the case of bayonet-base 
lamps, which are manufactured without a resistor, the proper resistance 
must be supplied externally. The operating characteristics of several 
typical glow lamps are given in Table 6-6. 



Table 6-6 


. Operating Characteristics of a 


Typical 


Glow 


Lamp 






AVERAGE 








CO 






< 


in 
S3 






STARTING 








Q 






P^m'S 


TYPE 


RATED 
VOLTS 


VOLTS* 




pa 


BASE 


O 

H 

u 

w 


RESIST- 
ANCE 


GAS 




< J 2 








i-' 






A.C. 


D.C. 


< 

0.25 


P 
T-4£ 












< 


AR-3 


(105-1251 


80 


115 


Cand. screw 


P-3 


In base 


Argon 


Is 


1,000 




A.C.f 1 






















AR-5 


1 105-125 f 
lA.C.f J 


SO 


115 


0.25 


T-4^ 


Blue slide 


P-3 


In base 
(20,000 
ohms) 


Argon 


1ft 


3,000 


NE-2 


105-125 


65 


90 


0.04 


T-2 


Unbased§ 


W-ll 


External 


Neon 


1ft t 


25,000 


NE-3 


105-125 


65 


90 


0.04 


T-2 


Unbased§ 


W-ll 


In lead 


Neon 


lftt 


3,000 


NE-16 


105-125 




67-87|| 


0.25 


T-4J 


D-c. bay. 


P-3 


External 


Neon 


1-2- 


3,000 


NE-20 


105-125 


60 


85 


1.00 


G-10 


Med. screw 


PW-5 


In base 


Neon 


2A 


3,000 


Fluores- 


110-125 


100 


140 


1.00 


S-ll 


Two-prong 










3,000 


cent 


A.C. 










or med. 
screw 












Fluores- 


110-140 


100 


140 




G-6 


Cand. screw 


W-10 


50,000 


Krypton 




3,000 


cent 


A.C. 














ohms 








KR-1 


150-175 
D.C. 






















Fluores- 


110-125 






4 


G-16 


Candelabra 


Special 






31 


1,000 


cent 












skirted 












Xmas 












screw 












tree 

























* At hours operation. 
t May be operated on 135-volt, d-c circuits. 
t Glass parts only. 

§ Lamps have wire terminals f«-inch long not included in MOA length, 
set into one lead wire &-inch from end of glass seal. 

|| Direct-current operating voltage at 1.5 milliamperes, 53-65 volts. 



Resistance where specified is 



LIGHT SOURCES 



6-29 



Argon, Neon, and fluorescent glow lamps are available. In the fluorescent 
type the energy output of the discharge in the 0.01 to 0.1 micron wavelength 
Schuman ultraviolet region is sufficiently independent of ordinary ambient 
temperatures that these lamps may be operated satisfactorily out of doors 
in winter weather. 

Crater lamps. These lamps, shown in Fig. 6-22, emit the characteristic 
lines of the neon spectrum from an arc between the central "crater" 
cathodes and the surrounding ring anode. They operate in series with a 
ballast resistor on direct current; their output may be modulated rapidly. 

Concentrated-arc lamps. These lamps are a type of direct-current dis- 
charge lamp made with permanent, fixed electrodes sealed into an argon- 
filled glass bulb. The light source is a small spot (0.003 to 0.059 inch in 
diameter) of incandescent zirconium which forms on the end of a zircon- 
ium-oxide-filled tantalum tube, (the negative electrode). See Fig. 6-23. 




FIG. 6-23. Concentrated arc lamps. 

The radiation is distributed throughout the visible, ultraviolet, and 
infrared portions of the spectrum between 0.3 and 4.0 microns and has a 
cosine type of spatial distribution. 27 

Special starting and operating circuits, including a resistance ballast, 
are required. See Table 6-7. 

Table 6-7. Operating Data on Standard Sizes of Concentrated- Arc Lamps 



NOMI- 
NAL 

LAMP 
RAT- 
ING 

(watts) 


VOLTS 


AM- 
PERES 


LIGHT 
SOURCE 
DIAM- 
ETER 

(inches) 


BRIGHTNESS 

(candles per 
square inch) 


MAXI- 
MUM 
CAN- 
DLE 

POWER 


LIFE* 

(hours) 


BULB 


BASE 


MAXIMUM 
TEMPERA- 
TURE 

(degrees F) 


Maxi- 
mum 


Aver- 
age 


Type 


No. 
Pins 


Bulb 


Base 


2 


37 


0.055 


0.003 


62,000 


36,000 


0.32 


175 


T-5 


Min. 3 


140 


100 


10 


21 


0.5 


0.016 


35,400 


14,200 


2.7 


700 


T-9 


Small 8 


225 


130 


25 


20 


1.25 


0.029 


26,000 


13,600 


8.7 


800 


T-9 


Small 8 


355 


145 


100 


15.4 


6.25 


0.059 


33,600 


25,200 


77.0 


1,000 


ST-19 


Med. 4 


470 


160 



* Average life obtained under laboratory conditions. 



6-30 



I E S LIGHTING HANDBOOK 



Flashlamps or flashtubes. As their name suggests these lamps are de- 
signed to produce high brightness flashes of light of extremely short dura- 
tion. A flashlamp is a tube of glass or quartz which has an electrode in 
each end. The tube is filled with gas, usually xenon. The spectral 
distribution of light from an xenon discharge is similar to that of average 
daylight. (See Fig. 6-24.) Other gases employed include argon, hydro- 
gen, and krypton. Typical time-light curves for xenon-filled lamps are 
shown in Fig. 6-25. 



| 60 

Q 

2 55 

LU 
I- 
(/) 

a: 50 
in 

Q_ 
1045 

HI 

_) 

O 
O40 

_J 

3 35 













































/ 














' 











































FIG. 6-24. Spectral energy 
distribution curve of typical 
xenon-filled flash lamp (radiation 
in direction perpendicular to 
helix). 

1 micron = i0,000 angstroms = 1/10,000 
centimeter 



0.45 0.50 0.55 0.60 0.65 0.70 
WAVELENGTH IN MICRONS 



20 




r\ 


























// 
// 
u 


r \ 




\ VOLTS AT 
-X 56 MF 


















15 




































%o 


, 






















10 










\ 
\ 
\ 








/_ MF AT 1800 
S°« VOLTS 










1 
1 
1 


i 








\ 




s^ 


<? 














5 


II 
IV 




N 


\ 




v 56 


















\\ 

lis'' 

if 


-X'tpoS 


\,. 


-28 " 


\. v. 


S^ 



















r" 


'000~ 

1 


15 


S^s 


~-- 


-----_- 




^** — 


--_-_ 


r-_- 


-_-vr. 


= --- 


.__ 



100 200 300 400 500 600 700 

TIME IN MICROSECONDS 

FIG. 6-25. Time-light curves for a flash lamp at various ca- 
pacitance and voltage levels. 

Several straight tubular lamps have been developed for use in trough 
reflectors. For most applications, however, more concentrated forms are 
preferred. As with tungsten filaments, improved concentration is ob- 
tained by coiling the tube in the form of a helix. Three sizes of helices 
have been used with different bulb and base combinations to make the 
typical lamps shown in Fig. 6-26. Lamps differ in types and sizes of elec- 
trodes, type of gas with which the tube is filled, filling pressure, and tube 
material; also, different electrical circuits are used for flashing the lamps. 28 



LIGHT SOURCES 



6-31 




FIG. 6-26. Flash lamps mounted in typical enclosures. 

Power supply. The basic elements include a step-up transformer and 
a rectifier to obtain the high-voltage direct current required to charge the 
condenser and some means of limiting the charging current of the con- 
denser to the safe limits of the rectifying tubes and transformers. This 
limiter may be either a resistor or reactor connected in series with the 
condenser on the charging side or a high-leakage reactance characteristic 
in the step-up transformer itself. A typical circuit is shown in Fig. 6-27.. 



RECTIFIER 



FLASHTUBE 




FIG. 6-27. Basic elements of typical flash-lamp power supply. 

In one type of flashing circuit an extremely high potential (of the order 
of 10,000 volts or more) is momentaiily applied to the wall of the tube, 
producing a brilliant flash of light of extremely short duration. When the 
condenser charge has been almost entirely expended, the voltage across the 
terminals drops to a low value, the tube ceases to conduct, and the con- 
denser proceeds to accumulate the charge required for the next flash. 

Another circuit utilizes flashlamps which operate without separate 
ionizing potential. In this type the lamp is not connected across the 
terminals of the condenser until it is desired to flash the tube and the tube 
itself is designed to flash over at the potential of the charge in the con- 
denser. The power-supply design is thus simplified, but it is necessary to 
employ a switch which can handle the high voltages and momentarily 
high currents involved. 

Limits of energy input. For single-flash operation, the limit to the 
amount of energy which can be consumed depends upon the desired lamp 



6-32 



I E S LIGHTING HANDBOOK 



life, that is, the total number of useful flashes. This is affected by the rate 
of tube blackening and destruction of the tube or its parts. 

If a flashtube is operated repetitively and rapidly at the maximum 
energy input level so that its temperature rises excessively, it will either 
miss (fail to flash) or become continuously conductive. In the latter case 
the tube may be damaged. The total watts consumed are the product of 
the watt-seconds per flash and the number of flashes per second. The 
figures for a tube operating at 2,000 volts and 112 microfarads (224 watt- 
seconds per flash) are tabulated below for different rates of flash : 

Input to Lamp 
Flashing Rate (Watts) 

One flash per minute 3.7 

One flash per 10 seconds 22.4 

One flash per second 224.0 

Ten flashes per second 2240 . 

One hundred flashes per second 22,400.0 

Where repetitive flashing is necessary the power input per flash to the 
tube must be reduced as the rate of flashing; is increased. 



FLUORESCENT LIGHT SOURCES 

Fluorescent light sources which emit light in a variety of colors include 
the mass-produced types (Fig. 6-28) and custom-made types also. Both 
utilize cylindrical glass tubing coated inside with fluorescent phosphors. In 
each type an electrode is sealed in at each end and, after evacuation of the 
tube, a small drop of mercury is added and a volume of neon or argon is 
introduced at low pressure (3 to 18 millimeters of mercury, depending on the 
lamp). 



TUBE FILLED WITH ARGON GAS 
AND MERCURY VAPOR 



CATHODE COATED 
WITH ELECTRON- 
EMISSIVE MATERIAL 



ANODE 




INSIDE OF TUBE COATED WITH 
FLUORESCENT PHOSPHORS 



-BASE CEMENT 
>BASE PINS 

a 



STEM 
PRESS 



EXHAUST 
TUBE 






FIG. 6-28. Cutaway view of fluorescent lamps showing typical electrodes and 
bases : (a) filament (hot) cathodes (preheat starting) ; (b) filament (hot) and (c) cylin- 
drical (cold) cathodes (instant starting). 



LIGHT SOURCES 



6-33 



The relationship between mercury vapor pressure and current density 
inside a lamp and the voltage supplied by the electrical circuit is chosen 
so that under normal operating conditions the output of the arc discharge 
through a lamp is largely in the 0.2537-micron-wavelength ultraviolet- 
spectrum line, which is presently the most efficient in producing fluores- 
cence. 29 

Most of the many straight and circular lamp types mass-produced in 
the United States are standardized with respect to their nominal photo- 
metric, color, electrical, and mechanical characteristics. For the most 
part, different manufacturer's lamps of the standardized types are me- 
chanically and electrically interchangeable. 

Custom-made fluorescent lamps in several different diameters and 
colors are prepared on order in lengths and forms designed for a particular 
installation. 

Fluorescent sources are electric discharge lamps. Like all other dis- 
charge lamps, they have a negative resistance characteristic and therefore 
must be operated in series with a current-controlling ballast. The type 
designed for use on low- voltage circuits with a special manual or automatic 
starting switch requires a short (3-4 second) preheat period after closing 
the circuit before the arc strikes. Other types are designed for circuits 
which provide a higher starting voltage (400-15,000 volts). In these, the 
discharge starts instantly upon closing the circuit. 

Fluorescent lamp bases. For satisfactory performance, each fluorescent 
lamp must be connected to an electrical circuit with proper voltage and 
current characteristics for its type. Therefore, different lamps are made 
with different bases, as shown in Fig. 6-28. When the proper lamp hold- 
ers are wired to a particular type of ballast and properly spaced, only the 
lamp type for which that ballast was designed may be inserted in the cir- 
cuit. Typical lamp holders are shown in Fig. 6-29. 




FIG. 6-29. Typical holders for fluorescent lamps. 

Fluorescent lamp performance. Performance characteristics of fluores- 
cent lamps which are of general interest and importance include: 
Initial light output (lumens after 100 hours operation). 
Efficiency (lumens per watt consumed). 



6-34 



I E S LIGHTING HANDBOOK 



Lumen maintenance throughout life (per cent of initial value). 

Color (spectral distribution, I.C.I, co-ordinates). 

Speed and dependability of starting. 

Stroboscopic effect. Brightness (footlamberts). 

Radio interference. Useful life in service (hours). 

Data on typical lamps of a variety of types are given in Fig. 6-30 and 
in Tables 6-8, 6-9, and 6-10. So far as possible, data presented on types 
produced by several manufacturers represent industry averages. Since 
these data are likely to differ slightly from specific figures on one manu- 
facturer's product, it is advisable to check the manufacturer's data sheets 
for detailed information on current production. 30 



80 
60 

5 40 

5 20 

O 

> 

£100 

z 

m 80 

LU 

^60 

< 

w 40 

cr 

20 




0.8 





- 












BLUE 


















/ 


V 














/ 





























GREEN 










































\ 










1 






\ 


-^ 





















PINK 



































WHITE 




















tJl 

















n 










DAYLIGHT 


















> 


V 















0.38 0.45 0.50 0.55 0.60 0.65 0.70 0.76 0.38 0.45 0.50 0.55 0.60 0.65 0.70 0.76 1 

WAVELENGTH IN MICRONS 

1 micron = 10,000 angstroms= 1/10,000 centimeter 

FIG. 6-30. I.C.I, x-y co-ordinates and spectral distribution curves of light from 

typical fluorescent lamps. 



LIGHT SOURCES 



6-35 



Table 6-8. Performance Data on Typical Filament (Hot) Cathode, 
Preheat-Starting, Fluorescent Lamps* 



Approx. lamp wattsf 

Nominal length (inches)J. 

Bulbf| 

Base (bipin) 

Approx. lamp amperes . . . 

Approx. lamp volts ^ 

Max. starting amperes . . . . 



Rated life (hours)** 
and lumen main- 
tenance (per cent 
initial lumens) 
for daylight and 
white lamps at 
70% rated life 



hrs/ 

start 



Initial lumens: 

White 

Daylight. . . . 
Soft white . . 
4,500° white. 

Blue 

Green 

Yellow green 

Pink 

Gold 

Red 

Footlamberts: 

White 

Daylight... 
Soft white . . 
4,500° white 

Blue 

Green 

Pink 

Gold 

Red 



4 


6 


8 


13 


14 


15 


15 


20 


30 


32 


40 


6 


9 


12 


21 


15 


18 


18 


24 


36 


$ 


48 


T-5 


T-5 


T-5 


T-5 


T-12 


T-8 


T-12 


T-12 


T-8 


T-10 


T-12 


Min. 


Min. 


Min. 


Min. 


Med. 


Med. 


Med. 


Med. 


Med. 


4 pin 


Med. 


0.127 


0.152 


0.170 


0.160 


0.372 


0.302 


0.332 


0.357 


0.342 


0.42 


0.410 


36 


46 


57 


95 


42 


56 


48 


61 


103 


85 


107 


0.18 


0.24 


0.27 


0.27 


0.65 


0.65 


0.65 
2,500 


0.65 


0.65 


— 


0.75 


2,500 


2,500 


2,500 


2,500 


2,500 


2,500 


2,500 


2,500 


2,500 


2,500 




75% 


7 ccr 
' *> ,0 




85% 


78% 


84% 


84% 


78% 




84% 










4,000 


4,000 


4,000 


4,000 


1,600 


4,000 













72% 


V6% 


76% 


72% 




76% 










6,000 


6,000 


6,000 


6,000 




6,000 












69% 


70% 


70% 


69% 




70% 


73 


210 


330 


582 


490 


622 


600 


940 


1,485 


1,600 


2,310 


68 


185 


295 


505 


420 


555 


517 


800 


1,350 




1,960 










365 


487 


472 


720 


1,170 




1,760 




200 


310 


547 


460 


585 
315 
900 

300 

375 

45 


570 
300 
855 

2S5 

355 

42 


860 

460 

1,300 

1,080 

440 

540 

60 


1,380 

780 

2,250 

750 
930 
120 




2,110 
2,600 




2,615 


2,775 


2,690 


1,390 


2,060 


1,420 


1,515 


2,370 


2,040 


1,750 




2,345 


2,495 


2,330 


1,180 


1,905 


1,275 


1,330 


2,140 




1,570 










975 


1,560 


1,100 


1,175 


1,870 




1,373 




2,470 


2,770 


2,520 


1,310 


2,030 
1,125 
3,200 
1 , 050 
1,650 
160 


1,290 
750 

2,610 
720 
900 
110 


1,360 
850 

2,400 
800 

1,000 
110 


2,120 
1,350 
3,900 
1,300 
1,600 
210 




1,640 



3,000 
78% 



4,500 
72% 



6,500 
69% 



4,300 
3,900 
3,350 
4,000 



1,965 
1,840 
1,580 
1,915 



* Industry averages. Lack of complete data from all sources results in some discrepancies within 
the table, 

t Wattage consumed by auxiliary must be added to get total. 

t Includes lamp and two sockets. 

5 Circular lamp 12 inches diameter. 

f| Figures indicate maximum outside diameter in eighths of an inch. 

11 110- to 125-volt circuit ballasts available for all types, higher voltage ballasts for some. 

** Average life under specific test conditions. 



Table 6-9. Performance Data on Typical Filament 
Instant-Starting, Fluorescent Lamps* 



(Hot) Cathode 



Nominal length (inches)t 

Maximum lamp length (inches) 

Bulb designation^ 

Open circuit voltage 



Lamp current (milliamperes) . 
Rated life (3 hours operation 

per start) hours§ 

Lamp watts|| 

Approximate lamp volts 

Initial lumen output (white) . 
Footlamberts (white) 



40 
T-6 
450 



100 

2,500 
15 



200 

2,500 
26 



41 

2,500 
40 



62 
T-6 

600 



100 

2,500 
24 



200 



70 
T-8 

575 



100 



2,500 2,500 
39 22 



200 

2,500 
38 



96 



94 
T-8 

725 



100 

2,500 
29 



200 

2,500 
51 



175 

915 

1,680 



147 108 
1,400 2,300 
2,590 ! 1,750 



277 
1,410 
1,670 



230 
2,100 
2,560 



247 
1,405 
1,050 



217 
2,350 
1,755 



335 
1,920 
1,065 



292 
3,250 
1,790 



* Industry averages. t Figures indicate maximum outside diameter in eighths of an inch. 

t Includes lamp and two sockets. || Wattage consumed by auxiliary must be added to get total. 
J Six hours operation per start. 4,000 hours; twelve hours operation per start, 6,000 hours. 
II Same as 40-watt hot cathode lamp in table 6-8. 



6-36 



I E S LIGHTING HANDBOOK 



Table 6-10. 



Performance Data on Typical Cylindrical (Cold) Cathode, 
Instant-Starting, Fluorescent Lamps* 



OUT- 
SIDE 


OPER- 
ATING 
CUR- 
RENT 

(milli- 
amperes) 


COLOR 
DESIGNATION 


M M M BRIGHTNESS! 

woo (footlamberts) 

OOO 


INITIAL 

LU- 
MENS/ 
FOOT! 
(100-hr 
oper- 
ation) 


H 
O 
O 
(n 

CO 

H 
i-J 
O 
> 


H 

o 
o 

fa 

CO 

< 


LUMEN MAINTENANCE 
(per cent initial lumens/foot) 


ETERf 

(milli- 
meters) 


8J 


§1 


si 

o — 


00 


<= 3 




24 


3,500° White 
Daylight^ 
Warm white 


74 

71 
SO 


63 


1.5 




25 


48 


3,500° white 

Daylight^ 
Warm white 


550 
500 
600 


142 
132 
150 


57 


2.7 














96 


3,500° white 
Daylight If 
Warm white 


1,150 
1,050 
1,200 


271 
247 
286 


50 


4.8 


87 
87 
87 


84 
84 
84 


81 
81 
81 


78 

78 
78 


75 

75 
75 




24 


3,500° white 
Daylight! 
Warm white 


460 
430 
500 


87 
80 
94 


72 


1.7 












20 


48 


3,500° white 

Daylight^ 
Warm white 


950 

850 

1,000 


172 
159 

184 


64 


3.1 


93 

93 
93 


89 
89 
89 


87 
87 
87 


85 
85 
85 


83 
83 

83 




96 


3,500° white 
Daylight! 
Warm white 


1,700 
1.500 
1,850 


322 
299 
339 


57 


5.5 














24 


3,500° white 
Daylight If 
Warm whit 3 


860 
780 

870 


108 

98 

110 


90 


2.2 












15 


4S 


3,500° white 
Daylight^ 
Warm white 


1,400 
1,350 
1,500 


190 
172 
203 


81 


3.9 













* Industry averages supplied by the Fluorescent Lighting Association. 

t Optimum pressure-diameter relationships with respect to the lumen output, life, and voltage of cylindri- 
cal (cold) cathode fluorescent lamps have been standardized by the Fluorescent Lighting Association along 
with over-all lengths of these lamps. 31 



FLUORESCENT LIGHTING ASSOCIATION STANDARDS 





7 




8 


9 


10 


12 


15 


18 


20 1 25 








Pressure (mm of mercury) 


IS 


17 


15 


13 


11 


9 


8 


7 J 6 


Over-all length (inches) (Subtract 4 to get lum- 
inous length) 


52 


64 


76 


| 


84 


93 


116 



t For gases No. 1050, No. 50, or No. BIO at standard pressure (for argon multiply by 0.96). For Argon at 
4-millimeter pressure multiply by 0.87. 

§ For luminous portion (over-all less 4 inches), assuming lamp power factor equals 100 per cent and neg- 
lecting voltage drop, wattage loss at electrodes, and ballast watts: To get over-all lamp voltage multiply volts 
per foot by length of luminous portion and add 105 (approximate electrode drop). To get total watts con- 
sumed by lamp and ballast multiply watts per foot by length of luminous portion and add both (voltage 
loss at electrodes 105 x operating current) and the ballast watts. 

K Applies to soft white also. 



LIGHT SOURCES 



6-37 



Factors affecting fluorescent lamp performance. A number of variables 
have an appreciable effect on fluorescent lamp performance. As noted 
below these include external factors as well as design and manufacturing 
details: 

Lamp current. 

Bulb-wall temperature. 

Ambient temperature. 

Mercury vapor pressure. 



Dimensions. 

Electrodes. 

Inert-gas filling pressure. 

Lamp voltage. 



Humidity. 
Surface treatment. 
Hours in operation. 
Auxiliary equipment. 



Arc watts per square inch of phosphor area. Hours operation per start. 
Fluorescent lamp light output and efficiency. 

Several energy conversions take place when light is produced by a fluores- 
cent lamp. As in other light sources today, a relatively small percentage of 
the power consumed is converted to light. See Fig. 6-31. 



LUMENS 
PER WATT 



If the energy in any light source could be converted without loss 
into yellow-green light (0.5540 micron") the efficiency of the source 
would be 62llumens per watt (100 per cent of the theoretical maximum). 



M.LZI 



174 



77 



r~ — 



_ But phosphors produce light over a range of wavelengths. When 
\ combined to produce the standard 3500°white color the average 
luminosity is 47 per cent of the maximum. 



^ Of the_40 watts delivered to the lamp 60 per cent is converted to exciting 
<£2 ultraviolet. Most of the balance goes info electrode heating and bulb warn 



jrmth. 



The conversion from the ultraviolet wavelength (0.2537 micron) to the visible wave- 
lengths which make up the 3,500° white color, is accomplished by the phosphor at the 
theoretical maximum efficiency (44 per cent) known as the quantum ratio. 




Losses from coating absorption, bulb absorption, end loss in brightness and non- 
utflization of 2,537 total 14 per cent. (86 per cent efficiency). 



53 Phosphor 

5 Visible mercury lines 
58 Rated efficiency 



The 18 per cent loss frorm65 to 53 lumens 
per watt results from depreciation in first 
100 hours operation, phosphor imperfection 
and loss in milling and miscellaneous manu- 
facturing variables. The phosphor and bulb 
transmit 5 lumens produced by visible 
mercury lines . 



ELECTRICAL ENERGY 
INPUT 



ENERGY 
CONVERSION 
WITHIN LAMP 





EXCITING ULTRAVIOLET 60% 
CONCENTRATED AT 2537A LINE' 



tf:#;.HEAT '38 t Vo-.V:*: 

[ELECTRODE HEATING: 
'•[••AND. BULB. WARMTH*. 



ENERGY 
OUTPUT 



FLUORESCENT POWDERS CONVERT : 
7.3 WATTS TO LIGHT 16.7 WATTS TO HEAT 

y -*: < 



15.1 WATTS 



LIGHT 
8.2 WATTS 
(20.5 %) 



RADIATED HEAT^-';V.v. CONVECTION 'AND' CONDUCTION:'-' 
'//.\0.% WATTS^% ::••.■■.'•:'■•.•".•'-••;• ::.'• TOTAL 21.2 WATTS: 



FIG. 6-31. Energy conversion efficiency and distribution in a typical preheat- 
starting, 40-watt, white fluorescent lamp. 



6-38 



I E S LIGHTING HANDBOOK 



Both design factors and operating conditions influence the efficiency 
with which the conversions take place and, therefore, the light output of 
any given lamp. Figuie 6-31 shows the energy distribution and conver- 
sion efficiency characteristic of one typical filament (hot) cathode, pre- 
heat-starting type of fluorescent lamp under optimum operating con- 
ditions. 

Arc length. Other things being equal, lumen -per-watt ratings of long 
lamps are greater than lumen -per-watt ratings of short lamps. Fig- 
ure 6-32 shows the relationship between arc length and lumen-per-watt 
ratings for t} r pical lamps. 




40 50 60 

ARC LENGTH IN INCHES 



FIG. 6-32. Curve a shows lumen-per-watt ratings as a function of arc length for 
typical white fluorescent lamps. Curve b shows the effect of auxiliaries for operat- 
ing preheat-starting lamps. Curve c shows the effect of auxiliaries for operating 
instant-starting lamps. The letter k indicates a cold cathode lamp. 

This arc length-efficiency relationship is a result of the power consumed 
at the electrodes (lamp current times electrode voltage drop). A drop of 
about 18 volts occurs at filament (hot) cathodes, and a drop of about 105 
volts occurs at cylindrical (cold) cathodes. Figure 6-33 shows the rela- 
tionship between lamp voltage and arc length for typical lamps. The 
characteristic electrode drops for the two types of cathodes is indicated 
by the intersect of the curves with the ordinate corresponding to zero 
length. 32 

Lamp current. Curves in Fig. 6-34 show the relationship between lu- 
mens per watt and lamp current in milliamperes for typical lamps with 
diameters of 1, 1^. and 2| inches. Anatysis of lamp dimensions and cur- 
rent at the peak in each curve indicates that maximum light production 
efficiency is obtained when the energy dissipated in the arc is about 0.13 
watt per square inch of phosphor area. 82 



LIGHT SOURCES 



6-39 



cfSU 
















1 
50 MA 




200 
















1 












48 IN. 






200 MA 




150 










\y 






350 
500 


VIA 












""'ix 






VIA 




100 




















15 IN: 


^18 IN. 
|J^ 






l 






TI2 
HOT CATHODE 


50 


















































450 



<5 

< 400 

















96 IN. jf 










T8 COLD CATHODE 
100 MA \ 


















72 IN. 




<^ 9 


5 IN. 
1/ 








48 IN. yr 




72 IN. 




1 














S 1 


<^1 


1 

1 








36 IN. 




\S 


*^J^ 


**^S 








8 IN. 








^^r T8 

HOT CATHODE 








1 y 




i 
















\ 



















350 
300 
250 
200 
150 
"100 

50 

-,__„. „ _ ._. .... - _ ,_ ,_ - .. 

10 20 30 40 50 60 70 80 90 100 
ARC LENGTH IN INCHES 

FIG. 6-33. Operating voltage of typical fluorescent 
lamps as a function of arc length. 




100 200 300 400 500 600 700 800 900 1,000 

LAMP CURRENT IN MILLIAMPERES 

FIG. 6-34. Lumen-per-watt ratings of typical white fluorescent 
lamps as a function of lamp current. 



6-40 



I E S LIGHTING HANDBOOK 



f a 



5wZ6 waW temperature. Under the operating conditions for which 
common lamps are designed (still air at 80 degrees Fahrenheit ambient 
temperature), 0.13 watt per square inch brings bulb-wall temperature to 
100 to 110 degrees Fahrenheit. 

The mercury vapor pressure (6 to 10 microns of mercury) related 
to this bulb-wall temperature is that at which the 0.2537-micron wave- 
length line is generated most efficiently. At lower bulb-wall temper- 
atures some of the mercury condenses and at the lower pressure 
the 0.2537-micron wavelength is produced less efficiently. At higher 
temperatures some of the energy radiated in the 0.2537-micron line is 
absorbed by the mercury vapor. 32 Therefore the lumen-per-watt rat- 
ing of a fluorescent lamp is affected by operating conditions which 
deviate from the 80-degree-Fahrenheit, still-air conditions to which 
the nominal lumen-per-watt rating applies. 33 

The change in bulb-wall 
temperature caused by air 
movement is shown in Fig. 
6-35 for exposed lamps, 
shielded lamps, and lamps 
enclosed in a glass sleeve. 
The change takes place as a 
function of the air speed and 
is independent of ambient 
temperature. 

The magnitude of the effect 
on light output of a change 
in bulb-wall temperature is 
not the same for all lamps, 
since, as shown in Fig. 6-36, 
not all are designed to have 
the 100-110 degree Fahrenheit 
wall temperatures associated 
with the optimum arc-power: 
phosphor-area ratio. 



20 



UJq; 

O uj 
Z Q_ 

< 2 

X UJ 

U l- 



30 



C 

6 

a 



2 4 6 8 10 12 

WIND IN MILES PER HOUR 



FIG. 6-35. The effect of air movement on 
fluorescent-lamp, bulb-wall temperature: (a) 
wind blowing directly on the lamp; (b) lamp 
shielded from the wind; (c) lamp enclosed in a 
glass sleeve $ inch larger in diameter. 



0.28 



0.24 



0.20 



0.12 



0.08 




FIG. 6-36. The incident radi- 
ant power density (arc watts per 
square inch) on the bulb wall 
determines the bulb-wall temper- 
ature of lamps of a given diam- 
eter operating in still air (80 
degrees Fahrenheit) at rated watts 
and amperes. 



80 90 100 110 120 130 140 

BULB-WALL TEMPERATURE IN DEGREES F 



LIGHT SOURCES 



6-41 



As shown in Fig. 6-37, the light output of lamps in groups A and B, 
which are designed to operate slightly above the optimum temperature 
under standard conditions, will increase slightly above rated values if 
the ambient temperature drops below 80 degrees Fahrenheit. A similar 
effect on the output of lamps in these groups will result from adduction in 
bulb-wall temperature caused by air movement. 



O 100 



Z 80 











RATING 


POINT 


GRC 


UP / 

a/ 












V 












' /c 




































20 40 60 80 100 120 

AMBIENT (ROOM) TEMPERATURE IN DEG F 

FIG. 6-37. Effect of ambient temperature on 
light output of the fluorescent lamps shown in 
Fig. 6-36 operating in still air at rated watts 
and current. 

Luminaires tend to confine or restrict the normal passage of air around 
a lamp and therefore cause an increase in the bulb-wall temperature. 
Data for typical luminaires are given in Fig. 6-38. 

zoo^ Jr\ M\ \5™7 AA 

a b c d e 

FIG. 6-38. Effect of typical luminaires on bulb-wall temperature of typical fluores- 
cent lamps: 33 

Temperature Rise 
Luminaire (Fahrenheit) 

o. Open end industrial (two 40-watt T-12 lamps) 15 

Closed end industrial (two 40-watt T-12 lamps) 20 

Closed end industrial with slots (two 40-watt T-12 lamps) 15 

Closed end industrial (three 40-watt T-12 lamps) 35 

b. Troffer, aluminum (one 40-watt T-12 lamp) 20 

Troffer, white (one 40-watt T-12 lamp) 20 

c. Troffer, shallow, with glass cover (two 40-watt T-12 lamps) 25 

d. TJ.R.C. glazed (four 40-watt T-12 lamps: inside lamps) 40 

e. Any luminaire, open top and bottom, lamps separated by baffle and/ 

or 6 inches apart 



6-42 I E S LIGHTING HANDBOOK 

Operation of ordinary lamps at low ambient temperatures and in loca- 
tions exposed to high winds results in below-optimum, bulb-wall tempera- 
tures and low lumen output per watt. However, a special lamp, designed 
and manufactured with a higher vapor pressure for operation at low tem- 
perature, may have quite good lumen output per watt under similar con- 
ditions. Starting difficulties encountered at low temperature with pre- 
heat-type lamps may be minimized by the use of a thermal switch starter. 

Hours in operation. Like that of other light sources, the lumen out- 
put of fluorescent lamps decreases as the hours the lamps are operated 
increase. Although the exact nature of the change of the phosphor 
which causes the phenomenon is not understood, it is known that at least 
during the first 4,000 hours of operation the reduction in lumen output 
per watt is directly related to the arc-power: phosphor-area ratio. 32 This 
relationship in several typical lamps is shown in Fig. 6-39a. As would be 
expected, lamps with different arc power-phosphor area ratios have differ- 
ent lumen maintenance curves, as shown in Fig. 6-396. 

Fluorescent lamp life and lamp starting. 

Hours operation per start. The oxide cathode coating must be in good 
condition to ensure proper starting at rated voltage of the preheat-starting 
fluorescent lamp. However, each time a preheat-type lamp is started a 
small amount of the oxide coating is consumed. A sufficient quantity of 
the material may be removed in about one thousand starts to cause starting 
failures. For this reason, the average life of these lamps is rated on the 
basis of hours operation per start. See Tables 6-9 and 6-10. 

Because the proper starting of cylindrical (cold) cathode lamps depends 
primarily on a high voltage rather than on the oxide coating of the cathodes, 
the life of this type of lamp is not appreciably affected by starting frequency. 

Effect of voltage and humidity on starting. To start a fluorescent lamp 
requires a higher voltage than is necessary to keep the lamp in operation 
once it has been started. Although all aspects of starting phenomena have 
not been explained, it is believed, on the basis of one theory which fits the 
available experimental data reasonably well, that capacitive current in the 
lamp is a necessary prerequisite to starting of the lamps now available. 34 

The two methods used are called preheat ("hot") starting and instant 
("cold") starting. The usual sequences are: 

Preheat starting: (a) A heating current is passed through the electrodes 
and electrons are ejected from the electrodes by thermionic emission, 
(b) Upon the application of a transient (600-1,200 volts) provided by the 
ballast and timed by a manual or automatic starting switch, electrons will 
flow through the tube, ionize the gases, and initiate a mercury vapor dis- 
charge. 

Instant starting: (a) By the application of a high open circuit voltage 
(400-3,000 volts depending on the type of lamp and electrode) electrons 
are ejected by field emission from the electrodes, (b) Electrons will flow 
through the tube, ionize the gases, and initiate a mercury vapor discharge. 

The high-voltage transient induced by rapid dissipation of the ballast 
magnetic field upon separation of the contacts of the starter switches 



LIGHT SOURCES 



6-43 



FIG. 6-39 a. Lumen 



maintenance curves for w 



120 



100 



z 80 



typical T-8 and T-12 
lamps, b. The reduc- 
tion in the lumen output 
of typical fluorescent 
lamps which accompa- 
nies the operation of 
the lamps is related 
directly to the incident \ 
radiant power density 2 
(arc watts per square g 
inch) on the phosphor 2 
surface. -i 



2] .60 

Q. 



1 














a 


^^ 


J££40TI2 



































10 
LIFE 



15 20 25 30 

IN HUNDREDS OF HOURS 



35 



40 




0.04 0.08 0.12 0.16 0.20 0.24 0.28 0.32 
ARC WATTS PER SO. IN. OF PHOSPHOR AREA 

used with preheat-starting filament (hot) cathode lamps is sufficient to 
initiate a glow discharge in a properly preheated and normally operable 
lamp of this type. The high open-circuit voltage of ballasts designed for 
instant-starting, cylindrical (cold) cathodes is sufficient to cause the glow 
discharge without preheating. Humidity ordinarily has no practical effect 
on the starting of the preheat and the cylindrical cathode lamps. 

In the case of filament cathode lamps designed for instant starting at the 
400 to 800-volts open circuit provided by "shock-type" ballasts, it is neces- 
sary to provide some means of counteracting the effect of high humidity 
on the capacitive lamp-ground current which initiates the necessary glow 
discharge under low humidity conditions. Some manufacturers coat the 
outside of the bulb of this type of lamp with a transparent, non wetting 
material; others apply a narrow conducting strip along the bulb. A con- 
ducting plate such as a metal reflector near the lamp appears to be ad- 
vantageous in some cases. 34 

Miscellaneous Fluorescent Lamp Characteristics. 

Stroboscopic effect. As indicated in Table 6-11, it is characteristic of 
light sources operated on alternating current that there is some light out- 
put variation of magnitude dependent on the cyclic variations of the cur- 
rent (lower frequency-greater variation). With incandescent lamps this 
is generally negligible since the filament retains enough heat to compen- 
sate for the variation of current throughout each cycle. With fluorescent 
lamps, the carry-over of light depends on the phosphorescent qualities of 
the coating. This characteristic of the phosphors varies considerably. 



6-44 



I E S LIGHTING HANDBOOK 



Table 6-11. Approximate Stroboscopic Effect of Fluorescent Lamps, 
Operated on 60-Cycle Circuits* 



Davlight 55 

White _. 35 

Daylight (two-lamp auxiliary) 25 

White (two-lamp auxiliary) 16 

Blue 90 

Gold 25 



Green 20 

Pink 20 

Red 10 

40-watt filament lamp 13 

100-watt filament lamp 5 



* Per cent deviation from mean light output. 

Two-lamp, lead-lag ballasts which are available for both hot and cold 
cathode types reduce this stroboscopic effect to a point where in ordinary 
two-lamp applications it is negligible. However, it may be an important 
consideration where moving objects are viewed or where the eye itself is 
moving rapidly. Further reductions may be made by three-phase opera- 
tion of three adjacent lamps or pairs of lamps. 

Radio interference. The mercury arc in a fluorescent lamp as well as 
other discharge sources causes a sparking action at the electrodes which 
emits low-power radio waves. These waves may be picked up and ampli- 
fied by near-by radios and cause a buzzing noise to be superimposed on 
the music or speech from the broadcasting station. The sound usually 
is more noticeable between stations on the dial but may be heard over the 
entire broadcast band. 

To ascertain if the fluorescent lamps are causing radio interference, tune 
the radio to a point where the interference is most pronounced, and then 
turn off the fluorescent luminaires. If the noise persists, it is from some 
source other than the fluorescent lamps. However, if the noise stops, it 
probably is caused by radio-frequency emission from the fluorescent lamps 
or auxiliaries. If the radio aerial must remain within about 10 feet of 
fluorescent lamps, the interference can usually be reduced by performing 
the following operations: (1) connect the aerial to the radio by means of 
a shielded lead-in wire with the shield grounded, or install a "doublet"- 
type aerial with twisted pair leads; (2) provide a good radio-frequency 
ground for the radio; (3) place the aerial itself out of bulb and line radia- 
tion range; (4) use an outside aerial to provide a strong radio signal. 

Circuits and auxiliary equipment for fluorescent lamps. 

Present types of fluorescent lamps must be operated on circuits which 
include current control reactance in series with the lamp. High open- 
circuit voltage or a high transient voltage must be provided by the circuit 
in order to start a lamp. 

As shown in Fig. 6-32, this auxiliary equipment consumes power and 
therefore reduces the over-all lumen-per-watt rating below that based 
on the power consumed by the lamp alone. 

The high open-circuit voltage associated with cylindrical (cold) cathode, 
instant-starting fluorescent lamps makes it possible to control the light 
output of this type by varying the current. The light output of these 
lamps may be "dimmed" smoothly down to about 10 to 15 per cent of the 
maximum. 



LIGHT SOURCES 



6-45 



High voltage may also constitute a safety hazard and various protective 
devices are used to prevent people from coming in contact with an open 
circuit. 

Power factor correction for fluorescent-lamp ballasts. Inherent charac- 
teristics of leakage reactance transformers result in a low power factor. 

The true watts of a low-power-factor transformer are approximately 
the same as the true watts of the high-power-factor type when connected 
to the same load. The low-power-factor type of transformer draws more 
current from the power supply, and, therefore, larger supply conductors 
are necessary than when using high-power-factor-type transformers. Some 
public utilities supplying power have established in their rate schedules 
penalty clauses for low-power-factor installations and bonus clauses for 
high-power-factor installations. The use of high-power-factor transform- 
ers permits greater loads to be carried by existing wiring systems. 

Typical power-factor-corrected circuits for preheat-starting lamps are 
shown in Fig. 6-40o(l) and (2). 

The power factor of existing instant-starting ballast installations for 
cylindrical (cold) cathode lamps can be corrected to the desired value by 
use of condensers connected across the primary supply lines between the 
primary switch and the load (Fig. 6-40, b). The use of a capacitor trans- 
former as in circuit 2 of Fig. 6-40 b), usually is less expensive, as the effect 
of condenser capacity varies as the square of the voltage applied across 
its terminals. The capacitor transformer is of "auto"-type construction 
with extended winding depending on the voltage rating of the condenser. 




© 



T 



TO LAMP 
LOAD 



LOW POWER FACTOR 
TRANSFORMERS 



LINE 



LINE 




HIGH POWER 

FACTOR 

TRANSFORMER 



FIG. 6-40. Typical power factor correction methods: a. Preheat-starting, fila- 
ment-cathode lamp circuits (l) two-lamp ballast with integral condenser; © single- 
lamp ballast with condenser, b. Instant starting cylindrical (cold) cathode lamp 
circuits; ® condenser; © capacitor transformer; (§) integral condenser in high 
power factor transformer. 



6-46 I E S LIGHTING HANDBOOK 

For example, if a condenser capacity of 16 microfarads is required at 110 
volts to correct the power factor to a desired value, the capacity can be 
reduced to 1 microfarad if 440 volts are applied to the condenser ter- 
minals. In new installations high-power-factor transformers should be 
used. This type is shown in circuit 3 of Fig. 6-40,6. The primary wind- 
ing is extended to a value three to six times the input voltage in order to 
reduce the condenser capacity. 

Preheat starting switches. 

In a preheat circuit a switch completes a series circuit so a preheat cur- 
rent can flow through the filament cathodes and heat them, and then breaks 
this circuit so that the resulting transient voltage from the ballast will 
start the lamp. The ballast permits a limited current to flow through 
the cathode filaments, which heats the filaments slowly (usually this takes 
about a second, as compared with 0.0001 second for heating an incandes- 
cent lamp filament). Several seconds ma}^ elapse before the entire start- 
ing operation is complete. A small (0.006 microfarad) condenser across 
the switch contacts aids in starting but is primarily useful in shunting out 
line-lead harmonics which may cause radio interference. The simplest 
concept of a starter switch is a push button which may be held down for a 
second or two and released. This type is used for desk-type fluorescent 
luminaires and also with the two-14-watt lamp circuit. The starters 
described below represent several designs for accomplishing the operation 
automatically. 

Thermal-switch starter. On starting, the ballast, starter heating ele- 
ment, and lamp cathodes are in series across the line. The contacts of 
thermal -switch starters normally are closed, as shown in Fig. 6-41a. The 
cathode preheating current also heats the bimetallic strip in the starter, 
causing the contacts to open. The induced voltage then starts the lamp, 
the normal operating current holding the thermal switch open thereafter. 

Thermal-switch starters consume some power (| to 1^ watts) during 
lamp operation, but their design ensures more positive starting by pro- 
viding: (1) an adequate preheating period, (2) a higher induced starting 
voltage, and (3) characteristics inherently less susceptible to line-voltage 
variations. For these reasons they give best all-around performance of 
40-watt lamps, being especially useful under adverse conditions such as 
direct-current operation, low ambient temperature, and varying voltage. 

Glow switch starter. The glass bulb shown in Fig. 6-416 is filled 
with neon, helium, or argon, depending on the lamp size. On starting, 
when there is practically no voltage drop at the ballast, the voltage at the 
starter is sufficient to produce a glow discharge between the U-shaped 
bimetallic strip and the fixed contact or center electrode. The heat from 
the glow activates the bimetallic strip, the contacts close, and cathode 
preheating begins. This short-circuits the glow discharge, so the bimetal 
cools and in a very short time the contacts open. The transient voltage 
thus induced is sufficient to start the lamp. During normal operation, 
there is not enough voltage across the lamp to produce further starter 
glow so the contacts remain open and the starter consumes no power. 



LIGHT SOURCES 



6-47 



CARBON 
RESISTOR 



SILVER 
CONTACT " 



S!h 



__ U-SHAPED 
BIMETAL 



CARBON 
CONTACT 



-r THIRD 

CONTACT 



m 



FIXED 
CONTACT 
(ELECTRODE) 



BIMETALLIC 

CONTACT 
(ELECTRODE) 



LINE 




RESET BUTTON 



CIRCUIT-BREAKER 
.CONTACTS 

t— BIMETAL 




LINE 



FIG. 6-41. Starter switches for preheat cathode circuits: (a) thermal type; (b) 
glow switch type; (c) manual reset type; (d) automatic reset type. 

Lockout starter. This starter, which may be either manual or auto- 
matic, is an improved glow switch which prevents the annoying blinking 
caused by repeated attempts to start a deactivated lamp. This type of 
starter should last for ten or more lamp renewals. 

Manual reset starter. This starter, shown in Fig. 6-41c, uses the 
glow-switch principle and, during normal starting, the switch functions 
in the manner that has been described. This starter has a wire-coil 
heater element actuating a bimetallic arm which serves as a latch to 
hold a second switch in a normal closed position. When a lamp is de- 
activated or will not start for some reason after repeated attempts and 
blinks on and off, enough heat is developed (after 15 to 20 seconds at rated 
line voltage) by the intermittent flow of cathode preheating current so 
that the latch pulls away and releases a spring-operated switch in the 
starter circuit. At the time the lamp is replaced, the starter may be re- 
set to operating position by pushing down on the reset button. 

Automatic reset starter. This type, shown in Fig. 6-41d, consists of a 
glow switch and additional bimetallic element which automatically opens 



6-48 



I E S LIGHTING HANDBOOK 



the glow switch circuit after a reasonable number of unsuccessful attempts 
to start a deactivated lamp. 

A low-resistance heater in series with the glow switch carries the start- 
ing current. As the switch attempts to start a deactivated lamp, the 
heater gradually heats the bimetal and opens the lockout contacts in the 
glow switch circuit. Open circuit voltage then exists across a resistor 
which is connected in parallel across these elements. This resistor con- 
sumes negligible power (less than one watt), but produces sufficient heat 
to hold the lockout contacts open. When the deactivated lamp is replaced, 
the starter automatically resets to its normal position, ready to function 
again. 

Typical circuits 

Several auxiliary circuits for operating fluorescent lamps in multiple and 
*n series are shown in Fig. 6-42. 



LINE SWITCH 



BALLAST LAMP 



LINE 
VOLTAGE 



TI2 14-WATT LAMPS 



0.006 MF RADIO- 
INTERFERENCE 
CAPACITORS 



3^ 



It 



D.P.S.T. MANUAL 
STARTING SWITCH 



D-C BALLAST 



O 




LINE VOLTAGE 



© a 



kSIMj- 



LAGGING SIDE 



LINE 
VOLTAGE 



LEADING SIDE 



i J - J 



a 



c- 



FIG. 6-42. Typical fluorescent lamp circuits: 21 a. Circuits for preheat-starting, 
filament-cathode lamps: © series circuit for 14-watt lamps with incandescent lamp 
resistance ballast and manual starting switch; © ballast for use on direct-current 
circuits, b. Two-lamp circuit for instant-start lamps on which the lamps are 
operated out of phase to minimize stroboscopic effect, c. Safety circuits for in- 
stant-start, cylindrical (cold) cathode lamp operation in interiors: © four-lamp, 
two-ballast circuit in which removal of a lamp-base cover disconnects transformer 
primary; © circuit developed by the Detroit Board of Education for use where 
lamps are subject to breakage; ® circuit for use in refrigerated showcases, d. 
Dimming-circuits for series-connected, cylindrical (cold) cathode lamps: ® vari- 
able resistance; © variable voltage transformer; ® saturable reactor. 



LIGHT SOURCES 



6-49 



NcJ 




— t--t 










:> 






A* 


♦ 










o. 















REMOVABLE 




FIXED 


! | f T" 


COVER fc 


r*ii ' 

1 Tll-l 

[ ►«? 


LAMP 




HOLDER 






REMOVABLE 
►' COVER 



- PRIMARY 
DISCONNECT 



O 



SECTION A-A 
(COVER RAISED TO 
BREAK THE CIRCUIT; 




MOMENTARY 
CONTACT SWITCH 



CURRENT 
TRANSFORMER 



© 




MOMENTARY * 
CONTACT SWITCH 



® 




VARIABLE-VOLTAGE 
TRANSFORMER 



6-50 



I E S LIGHTING HANDBOOK 



REFERENCES 



1. Merrill, G. S., "The Economics of Light Production with Incandescent Lamps," Trans. Ilium. Eng. 
Soc, December, 1937. Millar, P. S., "The Qualities of Incandescent Lamps," Elec. Eng., May, 1936; Dis- 
cussion, October, 1936. 

2. Merrill, G. S., "Voltage and Incandescent Electric Lighting," Proc. Intern. Ilium. Congr., Vol. II, page 
1494,1931. 

3. Hall, J. D., "The Manufacture of Incandescent Mazda Lamps," Elec. Eng., December, 1941. Millar, 
P. S., "Safeguarding the Quality of Incandescent Lamps," Trans. Ilium. Eng. Soc, November, 1931. "The 
Development of the Incandescenr^Electrie Lamp to 1879," Trans. Ilium. Eng. Soc, October, 1929. 

4. Langmuir, I., "Tungsten Lamps of High Efficiency," Trans. Am. Inst. Elec Engrs., October, 1913. 

5. Coolidge, W. D., "Ductile Tungsten," Trans. Am. Inst. Elec Engrs., May, 1910. 

6. Research Paper No. 502, National Bureau of Standards, Washington, D. C. 

7. Handbook of Interior Wiring Design, Industry Committee on Interior Wiring Design, 420 Lexington 
Avenue, New York, 1941. 

8. Prideaux, G. F., "Miniature Lamp Design and Applications," Cleveland Eng., December 6, 1945. 

9. Macbeth, N., "Color Temperature Classification of Natural and Artificial Illuminants," Trans. Ilium. 
Eng. Soc, March, 1928. 

10. Whittaker, J. D., "Applications of Silver Processed Incandescent Lamps with Technical Data," Trans. 
Ilium. Eng. Soc, May, 1933. 

11. Mili, Gjon, "Influence of Filament Form on Beam Characteristics with Shallow Paraboloid," Trans. 
Ilium. Eng. Soc, March, 1934. 

12. Carlson, F. E., "Light Source Requirements for Picture Projection," /. Soc. Motion Picture Engrs., 
March, 1935. 

13. Carlson, F. E., "Properties of Lamps and Optical Systems for Sound Reproduction Systems," J. Soc 
Motion Picture Engrs., July, 1939. 

14. Farnham, R. E., "The Lighting of Photochemical Reproduction Processes," Ilium. Eng., February, 
1941. 

15. Forsythe, W. E., "Light Sources for Color Photography," Photo Technique, June, 1939. 

16. Teele, R. P., "Gas Filled Lamps as Photometric Standards," Trans. Ilium. Eng. Soc, January, 1930. 

17. Hall, J. D., "Stop Vibration, Add to Lamp Life," Factory Management and Maintenance, October, 1940. 

18. Forsythe, W. E., "Arcs Their Operation and Light Output," Ilium. Eng., February, 1940. 

19. Bowditch, F. T., and Downes, A. C, "Spectral Distributions and Color Temperatures of the Radiant 
Energy from Carbon Arcs used in the Motion Picture Industry," J. Soc Motion Picture Engrs., April, 1938. 

20. Found, C. G., "Fundamentals of Electric Discharge Lamps," Trans. Ilium. Eng. Soc, February, 1938. 

21. Kronmiller, C. W., "Control Equipment for Discharge Type Lamps," Ilium. Eng., December, 1944. 

22. Buttolph, L. J., "The Characteristics of Gaseous Conduction Lamps and Light," Trans. Ilium. Eng. 
Soc, February, 1935. McMath, J. B., "Development and Use of Gaseous Conductor Tubes," Trans. Ilium. 
Eng. Soc, July, 1938. Rentschler, H. C, "Distribution of Light from Gas and Vapor Discharges," Trans. 
Ilium. Eng. Soc, June, 1934. 

23. Noel, E.B., "Radiation from High Pressure Mercury Arcs," Ilium. Eng., February, 1941. Marden, J. 
W., Meister, G., and Beese, N. C, "High Intensity Mercury Arc Lamps," Elec Eng., November, 1936. St. 
Louis, J. A., "Characteristics of 400-watt and 250-watt type H Mercury Lamps," Trans. Ilium. Eng. Soc, 
June, 1936. 

24. Noel, E. B., and Farnham, R. E., "A Water-Cooled Quartz Mercury Arc," J. Soc. Motion Picture 
Engrs., September, 1938. 

25. Fonda, G. R., and Young, A. H., "The A-c Sodium-vapor Lamp," Gen. Elec. Rev., July, 1934. Gordon, 
N. T., "Operating Characteristics of Sodium-vapor Lamps," Gen. Elec. Rev., July, 1934. 

26. Ferree, H. M., "Some Characteristics and Applications of Negative Glow Lamps," Trans. Am. Inst. 
Elec Engrs., January, 1941. 

27. Buckingham, W. D., and Deibert, C. R., "The Concentrated- Arc Lamp," J. Optical Soc. Am., June, 
1946. 

28. Carlson, F. E., and Pritchard, D. A., "The Characteristics and Application of Flash Tubes," Ilium. 
Eng., February, 1947. 

29. Townsend, M. A., "Electronics of the Fluorescent Lamp," Trans. Am. Inst. Elect. Engrs., August, 
1942. 

30. Amick, C. L., Fluorescent Lighting Manual, McGraw-Hill, New York, 1942. Forsythe, W.E., Barnes 
B. F., and Adams, E. Q., "Fluorescence and Fluorescent Lamps," J . Sci. Lab., Denison Univ. Bull., No. 36, 
April 1941. Inman, G. E., "Characteristics of Fluorescent Lamps," Trans. Ilium. Eng. Soc, January, 1939. 

31. Handbook of Cold Cathode Illumination, Fluorescent Lighting Association, New York, 1945. 

32. Lowery, E. F., Frohock, W. S., and Meyers, G. A., "Some Fluorescent Lamp Parameters and Their 
Effect on Lamp Performances," Ilium. Eng., December, 1946. 

33. Diefenthaler, R. J., and Forbes, J. C., "Effect of External Factors on Light Output of Fluorescent 
Sources," Ilium. Eng., December, 1946. 

34. Thayer, R. N., and Hinman, D. D., "Requirements for Reliable Instant Starting Fluorescent 
Lamps," Ilium. Eng., September, 1945. 

35. Mills, E. S., and Campbell, J. H., "Fluorscent Lamps and Radio Reception, Mag. of Light No. 5, 1940. 

36. Weitz, C. E., Electric Illuminants, International Textbook Co., Scranton, Pa. 



SECTION 7 



LIGHT CONTROL 

Once light has been produced by combustion, incandescence, gaseous 
discharge, fluorescence, or other means, the problem of primary impor- 
tance is its control. Light sources, such as flames or arcs, or incandescent, 
electric discharge, or fluorescent lamps, rarely are found to have the 
inherent characteristics of candlepower distribution, brightness, and color 
suited to direct application without control or modification. Also, cer- 
tain uncontrollable application conditions such as smoke, fog, condensa- 
tion of moisture, collection of dust, grease, and so forth may alter the 
characteristics of either lamp or luminaire in service. 

Modification of lamp characteristics or compensation for uncontrollable 
application conditions may be provided in a number of ways, all of which 
are examples of one or a combination of the following phenomena (which 
will be taken up in the order given here) : 



Reflection. Polarization. Diffusion. 

Refraction. Interference. Absorption. 

Diffraction. 

Light Path Phenomena 

Since most design problems may be solved by assuming light to be rep- 
resented by bundles of rays which travel along straight lines, this con- 
vention is used in this handbook. A few examples are given in small 
type of the methods used to explain the phenomena which take place as 
light is transmitted or reflected at the interface between mediums having 
different optical properties. These examples utilize the concept that 
light emanates from a source in the form of "wave fronts." The behavior 
of these wave fronts can be described graphically and used to explain 
various phenomena, involving principally a change in the direction of 
wave propagation. 1 ' 2i 3 

Wave motion may be represented graphically as shown in Fig. 7-1, the plot of the 
function 



Y = a sin 



■(4-f) 



where 



Y = displacement of particles from 

point P on the wave path (at 

time t) 
a = amplitude of the wave 
T = period of oscillation (time) 
x = distance along the wave path 

from origin to point P FIG. 7-1. Graphical representation 

X = wavelength of a plane wave. 

Phase differences between motions at points and P are equal to 2 n X/\; when 
X/\ is a whole number, the motions are in phase. 1 




Note: References are listed at the end of each section. 

1 



7-2 



I E S LIGHTING HANDBOOK 



Superposition of wave trains is illustrated by the three curves in Fig. 7-2. 

Wave fronts associated with waves emanating from a source of energy are the 
locus lines (see Fig. 7-3) of points in the wave train that move in phase. Wave 
fronts are perpendicular to their direction of propagation. 

Huygens' principle is the concept that each point in the wave front (pri- 
mary wave) is itself the source of secondary waves or wavelets. This 
principle may be applied, as in Fig. 7-4, to demonstrate how the front 
progresses along its path. 




FIG. 7-2. The superposition of the 
amplitudes of two individual wave 
trains (1 and 2) traveling in the same 
direction along one path results in a 
third disturbance (3) moving along 
the same path in that direction. 



(resultant) 



SOURCE 



WAVE 
TRAINS 




WAVE j^' 
FRONTS' 



FIG. 7-3. Wave fronts are the 
loci of points the motion of 
which is in phase. 




FIG. 7-4. New wave fronts may be 
constructed (Huygens' principle) by 
describing arcs of equal radius with 
centers at each point in the known 
front and drawing the curve (or sur- 
face) tangent to these arcs (or spheri- 
cal segments). 



LIGHT CONTROL 



7-3 



Reflection 

By reflection a medium redirects incident light beams. Reflection may 
be specular, spread, diffuse, or compound, and selective or nonselective. 
Reflection from the front of a glass plate is called "firsf-surface reflection 
and that from the back "second"-surface reflection. Refraction, diffu- 
sion, and absorption by supporting mediums are avoided in first-surface 
reflectors. 4 

1. Specular Reflection 

If a surface is polished (microscopically smooth) it reflects specularly, 
that is, the angle between the reflected ray and the normal to the surface 
will equal the angle between the incident ray and the normal, Fig. 7-5(a.) 

If two or more rays are reflected, these may form a virtual, erect, or 
inverted image of the source. A lateral reversal of the image occurs when 
odd numbers of plane mirrors are used, as in Fig. 7-5(6). The image is 
left-handed for an even number, right-handed for an odd number. 



SOURCE 




OBSERVER -^ 



FIG. 7-5. (a) The law of reflection states that the angle of incidence i = angle of 
reflection r. (b) A lateral reversal of the image accompanies reflections from an 
odd number of plane mirrors. 



Examples of specular reflectors 

1. Polished and electroplated metals* and first-surface silvered glass or 
plastic mirrors: Inside-aluminized, sealed-beam lamps and reflecting tele- 
scopes use first-surface reflectors in which the incident light strikes the 
thin metal reflecting surface without passing through the glass, as shown 



Silver, gold, or copper for example. 



7-4 



I E S LIGHTING HANDBOOK 



in Fig. 7-6(6). The function of the latter is simply to provide a rigid 
support for the reflecting surface. 

Applications: where accurate control is desired. 

Maintenance: smooth surface, easily cleaned. Materials such as pol- 
ished silver must be protected from the atmosphere. Others such as 
anodized aluminum may be exposed to ordinary atmospheres without 
serious depreciation. 

Light reflected from the upper surface of a glass plate, as in Fig. 7-6 (a) 
and (c), also is an example of first-surface reflection. As shown in Fig. 
7-8, less than 10 per cent of the incident light is reflected at the first sur- 
face unless it strikes the surface at wide angles from the normal. 

The sheen of silk and the shine from smooth or coated paper are images 
of light sources reflected in the first surface. Images of light sources and 
other objects seen in opaque polished glass store fronts and table tops, 
counter tops, and store windows are formed by first-surface reflections. 




FIG. 7-6. Reflections from (a) clear plate glass and (b) from front and (c) rear 
silvered mirrors. 



2. Rear-surface mirrors. Some light (the quantity depending on the 
incident angle) is reflected by the first surface. The rest goes through to 
the silvered backing and is reflected out through the glass, as shown in 
Fig. 7-6 (c), parallel to the ray reflected by the first surface (except for a 
small portion that is reflected internally at the first surface and emerges 
eventually as a third ray). This multiple reflection is of negligible effect 
in luminaires. The household mirror is one example of back-silvered, 
second-surface reflectors. 

3. One-way vision or half-silvered mirrors. These mirrors are coated 
with an extremely thin layer of silver or aluminum so that they are semi- 
transparent. When viewed against a comparatively dark background 
they appear to be ordinary mirrors, but it is possible to look through them 
into a brightly lighted area. The view is dim, and likely to be tinted 
with the characteristic color of light transmitted by the finely divided 
metal of the coating. 

Applications: where accurate control is desired but sharp images are 
nonessential. 

-. j Maintenance: the silvering is protected by glass; the smooth surface 
facilitates cleaning. 



LIGHT CONTROL 



7-5 



Reflection of a -plane wave from a 
specular plane surface. Figure 7-7 
indicates the angle of incidence i 
is equal to the angle of reflection r. 
Applying Huygens' principle, the 
construction is explained as fol- 
lows: 

1. Consider the line LL' as the 
plane specular reflecting surface. 

2. Let the line WW in position 
® represent the plane wave front 
approaching the surface in the di- 
rection indicated by the arrows 
perpendicular to the front (com- 
monly known as rays). 

3. Assume that at some time t 
the wave front, except for the pres- 
ence of the reflecting surface, would 
have progressed to position ®. 




L ^7777777777777777^77777^7^777^77 



REFLECTOR 






**^ 



FIG. 7-7. Reflection of a plane wave at a 
plane (specular) surface showing Huygens' 
construction of the new wave front. 



4. However, if the location of the front © is considered at some intermediate in- 
stant, it is found contact has been made with the surface at point P, from which a 
Huygens' wavelet has emanated at the same velocity as that of the primary wave at 
the instant of contact. 

5. Therefore, if an arc is described with center at P and radius equal to PX, the 
actual front of the new wavelet at time t has been established. It is a hemisphere 
on the air side of the reflector. 

6. By describing additional arcs at succeeding points of contact P' and P" with 
radii P'X' and P"X" (only two are necessary in the case of the plane wave) it is 
possible, by constructing the tangent to these arcs, to determine the actual position 
© of the primary wave front WW after reflection. 

In this manner the principle may be applied equally well to a reflection of plane 
or spherical waves from either plane or figured surfaces, tnough the construction 
is more complex. 3 Refraction may be explained a similar manner. 



FIG. 7-8. Effect of angle of 
incidence and state of polar- 
ization on per cent of light 
reflected at an air-glass* sur- 
face: (a) Incident light polar- 
ized in the plane of incidence, 
(b) Nonpolarized light, (c) 
Incident light polarized in 
plane perpendicular to plane of 
incidence. 



* Por spectacle crown glass, n = 1.523. 











































































































a/ 




































V 








BREWSTER'S 
ANGLE 2*. 






V 














Jl 















10 20 30 40 50 60 70 SO 
ANGLE OF INCIDENCE , Q , IN DEGREES 



7-6 



I E S LIGHTING HANDBOOK 



2. Spread Reflection 

If a surface is figured in any way (corrugated, deeply etched, or ham- 
mered) it spreads any rays it reflects, that is, a 'pencil of incident rays is 
spread out into a cone of reflected rays, as shown in Fig. 7-9(6). 






POLISHED SURFACE 
(SPECULAR) 



ROUGH SURFACE 
(SPREAD) 



C MAT SURFACE 
(DIFFUSE) 



FIG. 7-9. The type of reflection varies with different surfaces: (a) polished sur- 
face (specular); (6) rough surface (spread); (c) mat surface (diffuse). 

Spread reflectors. Depolished metals and similar surfaces reflect indi- 
vidual rays at slightly different angles but all in the same general direc- 
tion. 

Applications: where smooth beam and moderate control is required. 

Maintenance: collect dust and dirt more rapidly than smooth surface. 
Chemical cleaners often used. 

Corrugated, brushed, dimpled, etched, or pebbled surfaces consist of small 
specular surfaces in irregular planes. Brushing the surface spreads the 
image at right angles to the brushing. Pebbled, lightly hammered, or 
etched surfaces produce a random patch of highlights. 

Applications: where beams free from striations and filament images 
are required; widely used for sparkling displays. 

Maintenance: ease of cleaning depends on the shape and size of the 
indentations. 

3. Diffuse Reflection 

If a material has a rough surface or is composed of minute crystals or 
pigment particles, the reflection is diffuse. Each single ray falling on an 
infinitesimal particle obeys the laws of reflection, but, as the surfaces of 
the particles are in different planes, they reflect the light at many angles. 

With perfectly diffuse reflection (microscopic roughness: surface par- 
ticle diameters less than wavelength of light — seldom attained in practice) 
the reflected light distribution is independent of the angle at which the 
light strikes the surface. No matter what this angle may be, the maximum 
intensity of the light reflected is normal to the surface and the light is 
spread throughout an angle of 180 degrees. If the reflected beams are 
plotted, as in Fig. 7 -9(c), they will fill a circle (in three dimensions a 
sphere). This spherical distribution characteristic of perfectly diffuse 
reflected light is determined by the cosine law. The intensity (I ) at an 
angle (0) from the normal is proportional to the cosine of that angle: 

1/9 = ho° cos 



LIGHT CONTROL 



7-7 



Diffuse reflectors. Flat paints and other mat finishes and materials re- 
flect at all angles and exhibit little directional control. 

Applications: where wide distribution of light is desired. 

Maintenance: cleaning is often difficult since surfaces which approach 
microscopic roughness are likely to collect and hold dirt. 

4. Compound Reflection 

Most common materials are compound reflectors and exhibit all three 
reflection components (specular, spread, and diffuse). In some, one or 
two components predominate, as shown in Fig. 7-10. Specular and 
narrowly spread reflection (usually surface reflection) cause the "sheen" 
on etched or embossed aluminum, textiles, semigloss paint, snow fields, 
and so forth. 




a DIFFUSE AND SPECULAR 



b DIFFUSE AND SPREAD 



C SPECULAR AND SPREAD 



FIG. 7-10. Examples of compound reflection: (a) diffuse and specular; (b) diffuse 
and spread; (c) specular and spread. 

Diffuse-specular reflectors. Porcelain enamel, glossy paints, and enam- 
els and other surfaces with a shiny transparent finish over a mat base 
exhibit no directional control except for the specularly reflected ray that 
is shown in Fig. 7-10(a), which usually amounts to from 5 to 15 per cent of 
the incident light. 

Applications: diffusing reflectors. Bright source images make such 
finishes undesirable for walls and ceilings. 

Maintenance: glossy finish results in permanency of the reflecting sur- 
face and easy cleaning. 

Refraction 

A change in the velocity of light (speed of propagation, not frequency) 
occurs when a ray leaves one material and enters another of greater or less 
physical density. The speed will be reduced if the medium entered is 
more dense and increased if it is less dense. 3 

Except when light enters at an angle normal to the surface of a medium 
of different density, the change in speed always is accompanied by a 
bending of the light from its original path at the point of entrance, as 
shown in Fig. 7-11. This is known as refraction. The degree of bending 
depends on the relative densities of the two substances, on the wavelength 
of the light, and on the angle of incidence, being greater for large differ- 
ences in density than for small. The light is bent toward the normal to 
the surface when it enters a more dense medium and away from the normal 
when it enters a less dense material. One result of refraction is that the 



7-8 



I E S LIGHTING HANDBOOK 



ray path followed is that with the highest average velocity in any given 
case. FermaVs 'principle states that the total path will be the one which 
takes the least time to traverse. 

When light is transmitted from one medium to another, each single ray 
follows the law of refraction. When a pencil of rays strikes or enters a 
new medium the pencil may be broken up and scattered in many direc- 
tions because of irregularities of the surface, such as fine cracks, mold 
marks, scratches, or changes in contour, or because of foreign deposits of 
dirt, grease, or moisture. 



air (n=i) 




FIG. 7-11. Refraction of 
light rays at a plane surface 
causes bending of the inci- 
dent rays and displacement 
of the emergent rays. The 
bending and displacement is 
greater when the ray goes 
from a light to a dense medi- 
um than when it goes from 
a dense to a light medium. 



m 

i 



n 2 
r 



The law of refraction (Snell's law) is expressed: 

fti sin i = iii sin r 
where n\ = the index of refraction of the first medium 

the angle the incident light ray forms with the 
normal to the surface 

the index of refraction of the second medium 
= the angle the refracted light ray forms with 
the normal to the surface 
When the first medium is air, of which the index of refraction usually 
is assumed to be 1 (correct to three decimal places but actually the index 
for a vacuum) the formula becomes: 

sin i = iii sin r 

The two interfaces of the glass plate shown in Fig. 7-11 are parallel and 
therefore the entering and emerging rays also are parallel. The rays are 
displaced from each other because of refraction. 

Examples of refraction. A common example of refraction is the appar- 
ent bending of a straw at the point where it enters the water in a drinking 
glass. Although the straw is straight, light rays coming from that part 
of the straw under water are refracted when they pass from the water into 
the air and appear to come from higher points. Objects seen through 
window glass sometimes appear distorted as a result of the nonuniform 
thickness and flatness characteristic of window glass. These irregularities 
cause irregular refraction of transmitted raj^s and distortion of the images 
of objects at which the rays originate. 

Prismatic light directors, such as shown in Fig. 7-12(a) and (6), may be 
designed to provide a variety of light distributions for illumination pur- 
poses. 



LIGHT CONTROL 



7-9 






VERTICAL 
SECTION 



ELEVATION 



LIGHT 
SOURCE 
I 



OBJECTIVE 



EYEPIECE 




FIG 7-12. Optical systems utilizing the refractive properties of prisms and lenses: 
(a) Street-lighting unit in which the inner piece controls the light in vertical direc- 
tions (concentrating the rays into a narrow beam at about 75 degrees from the ^verti- 
cal) and the outer piece redirects the light in the horizontal plane. The result is a 
"two-way" type of candlepower distribution. (6) Prismatic lens for fluorescent 
lamp luminaire intercepts as much light as possible, redirecting part from the glare 
zone to more useful directions, (c) Cylindrical and flat Fresnel lenses (d) Lan- 
tern slide projector, (e) Astronomical telescope. (/) Galilean telescope, {g) 
Terrestrial telescope, (h) Reflecting prisms. 



7-10 



I E S LIGHTING HANDBOOK 



Lens systems controlling light by refraction are used in automobile 
headlights, in beacon, floodlight, and spotlight Fresnel lenses, in down- 
lights and in picture projectors, and in telescopes, field glasses, micro- 
scopes, and so forth, 4 as shown in Fig. 7-12. 

Compensation for abnormal vision is provided by spectacles, which 
utilize refractive properties of lenses to change the direction of light enter- 
ing the eye. 



RAY jARELY EMERGING 




Total reflection of a light ray 

at a surface of a transmitting 

medium occurs when the angle of 

incidence exceeds a certain value 

at which sin r becomes equal to 1 . 

If the index of refraction of the 

first medium (ni) is greater than 

that of the second medium (n 2 ), 

sin r will become unity when sin 

i is equal to w 2 /ni. At angles of 

___ M „„ _ . _ , incidence greater than this critical 

MG.7-13. total reflection occurs when i /.\ ,■. • -j 

. ,,,, ... , , . ... angle h e ) the incident rays are 

sin r = 1. 1 he critical angle i c varies with Jr . , . . „ . tv *, -.« 

the mediums. reflected totally, as m Fig. 7-13. 

In air when light strikes normally a piece of ordinary glass (w 2 /wi = 
0.6G) about 4 per cent is reflected from the upper surface and about 3 or 
4 per cent from the lower surface. Approximately 85 to 90 per cent of the 
light is transmitted and 2 to 8 per cent absorbed. The proportion of 
reflected light increases slowly as the angle of incidence is increased. In 
air total reflection occurs whenever sin i is greater than 0.66, that is, for 
all angles of incidence greater than 41.8 degrees (air— * glass). Both edge 
lighting and efficient light transmittance through rods and tubes are func- 
tions of total reflection. 5 See Fig. 7-8 b. 

Prisms. Many devices use total internal reflection by prisms for re- 
direction, inversion, and erection of light beams. Performance quality 
depends on flatness of reflecting surfaces, accuracy of prism angles, elimi- 
nation of back surface dirt in optical contact with the surface, and elimi- 
nation (in manufacture) of prismatic error. 

Dispersion of light by a prism. Consideration of Snell's law: 



n 2 = 



sin i Velocity of light in air 



sin r 



Velocity in prism 



suggests, since the velocity of light is a function of the index of refraction 
of the mediums involved and also of wavelength, that the exit path from a 
prism will be different for each wavelength of incident light and for each 
angle of incidence. (See Fig. 7-14.) This orderly separation of incident 
light into its spectrum of component wavelengths is called dispersion. 



LIGHT CONTROL 



7-11 



The angle of minimum deviation D is related to the prism angle A and 
to the index of refraction n 2 , as follows: 



sin 



n 2 = 



e-±-») 



AiR(n|) 



sin 



A 



however, if the prism angle 
is small, the approximations 

D _L 1 

n 2 = -j + 1, or 
A 

D = (n 2 - l)A 




FIG. 7-14. White light is dispersed 
into its component colors by refrac- 
tion when passed through a prism. 
Angle D is the angle of deviation. 



are reasonably accurate. See 
Fig. 7-14. 

Refractors and Refractor Materials 

Glass, transparent plastics, and quartz are used in the manufacture of 
refractive devices. 

Refracting prisms. The degree of bending of light at each prism sur- 
face is a function of the refractive indices of the two mediums and the 
prism angle. Light can be directed accurately within certain angles by 
having the proper angle between the prism faces. 

In the design of refracting equipment the same general considerations of 
proper flux distribution hold good as for the design of reflectors. Fol- 
lowing Snell's law of refraction the prism angles can be computed to pro- 
vide the proper deviation of the light rays from the source. For most 
commercially available transparent material like glass or plastics, the 
index of refraction used lies between 1.5 and 1.6. 

Often, by proper placement of the prisms, it is possible to limit the 
prismatic structure to only one surface of the refractor, leaving the other 
surface entirely smooth for easy maintenance. The number and the 
sizes of prisms used are governed by several considerations. Among them 
are ease of manufacture, convenient maintenance of lighting equipment in 
service, and so forth. A large number of small prisms may suffer from 
prism rounding in actual manufacture; on the other hand, small prisms 
produce greater accuracy of light control. 4 

Applications: headlight lenses, refracting luminaires, optical systems of 
scientific instruments. See Fig. 7-12(a), (6), (c) and (h). 

Ribbed and prismed surfaces can be designed to spread rays in one plane 
or scatter them in all directions. 

Applications: luminaires, footlight lenses, luminous elements, glass 
blocks, windows and skylights. 

Maintenance: smooth surface, easy to clean if prisms are not too small. 



7-12 



I E S LIGHTING HANDBOOK 



Reflecting prisms reflect light internally, as shown in Fig. 7 -12(h). 

Applications: luminaires, retrodirective markers. 

Maintenance: moisture, moist dirt, and grease in optical contact with 
surfaces reduce reflection ; smooth glass permits easy cleaning but must be 
cleaned on both surfaces (front and rear). 

Fresnel lenses. Excessive weight and cost of glass in large lenses used in 
illumination equipment can be reduced considerably by a method de- 
veloped by Fresnel. Several variations are used, as shown in Fig. 7 -12(c). 
The use of lens surfaces parallel to those replaced (shown by the dotted 
line) brings about a great reduction in thickness. The optical action is 
approximately the same. Although outside prisms are slightly more 
efficient, they are likely to collect more dust. Therefore, prismatic faces 
often are formed on the inside. 

Positive lenses form convergent beams and real inverted images as in 
Fig. 7-15(a). Negative lenses form divergent beams and virtual, inverted 
images as in Fig. 7-15(6). 




FIG. 7-15. 
Ray path traces 
through lenses: 

(a) positive, 

(b) negative. 



Lens aberrations. There are, in all, seven principal lens aberrations: 
spherical, coma, axial and lateral achromatism, astigmatism, curvature 
and distortion. Usually they arc of little importance in lenses used in 
common types of lighting equipment. In telescopic objectives and the 
like (small angular fields), the most important are spherical aberration, 
coma, and axial achromatism, which are illustrated in Fig. 7-16(a), (b) 
and (c). In such systems as photographic objectives (wide angular 
fields), astigmatism, curvature of field, and distortion also are important. 
These are shown in Fig. 7-16 (d) and (e). In modern telescopic and 
photographic lenses astigmatism and curvature usually are eliminated 
for all practical purposes and the lenses are likely to be complex. The 
simpler the lens system, the more difficult is the correction of the aber- 
rations. 6 



Transmittance and Transmitting Materials 

Transmittance is a characteristic exhibited to some degree by many 
materials: glass, plastics, textiles, crystals, and so forth. The luminous 
transmittance T of a material is the ratio of the total emitted light to the 
total incident light; it is affected by reflections at each surface of the ma- 
terial, as explained above, and by absorption within the material. 



LIGHT CONTROL 



7-13 



Bougefs or Lambert's law. Absorption in a clear transmitting medium 
is an exponentiarfunction of the thickness of the medium traversed: 

/ = H* 
where I = intensity of transmitted light. 

h = intensity of light entering the medium after 
surface reflection, 
t = transmittance of unit thickness. 
x = thickness of sample traversed. 

MARGINAL PARAXIAL 

ZONAL I 




foc«l Sm-n'ti Af rfoJ S al f rratloriS: (a) Spherical aberration: conversion at different 
rHffppfnn ■ ° f P ara J Iel ravs at varying distances from the axis of a lens. (6) Coma : 
len • (A rhthl?! 6ral ma S mficatlon of r rays passing through different zones of a 
eml'thi } M\ "XS \* dlffe f enCe ? f0 ^. length for rays of different wave- 
mntn«LiS;i? gI f at r m and . curvature : existence in two parallel planes of two 
mutually perpendicular line foci and a curved image plane, (e) Distortion- a differ- 
ence in the magnification of rays passing through a lens at different angles 



7-14 



I E S LIGHTING HANDBOOK 



Optical density (D) is the common logarithm of the reciprocal of trans- 
mittance (T): D = logio ( -J. 

Spread transmittance materials offer a wide range of textures, both when 
lighted from behind and when not. 

Applications: for brightness control as in frosted lamp bulbs, in lu- 
minous elements where accents of brilliance and sparkle are desired, and 
in moderately uniform brightness luminaire-enclosing globes. Care should 
be used in placing lamps to avoid glare and spotty appearance. 

Figure 7-17 (a) shows a beam of light striking the smooth side of a piece 
of etched glass. In Fig. 7-17(6) the frosted side is toward the source, a 
condition that with many ground or otherwise roughened glasses results 
in appreciably higher transmittance. 




FIG. 7-17. (a) Spread transmittance of light incident on smooth surface of figured, 
etched, ground, or hammered glass samples. (6) Spread transmittance of light in- 
cident on rough surface of the same samples, (c) Diffuse transmittance of light 
incident on solid opal and flashed opal glass, white plastic or marble sheet, (d) 
Mixed transmittance through opalescent glass. 

Maintenance: for outdoor use the rough surface usually must be en- 
closed to avoid excessive dirt collection. Etched surfaces are difficult to 
keep clean; smooth surfaces are easy to clean. 

Diffusing materials scatter light in all directions, as shown in Fig. 7-17(c). 
White, opal, and prismatic glassware are used widely. 

Applications: luminous areas where uniform brightness is desired. 

Maintenance: smooth surfaces minimize dust collection and permit 
easy cleaning. 

Mixed transmittance materials. Mixed transmittance is a result of a 
spectrally selective diffusion characteristic exhibited by certain materials 
such as fine opal glass, which permits the plane transmission of certain 
colors (wavelengths) while diffusing other wave-lengths. This character- 
istic in glass varies greatly, depending on such factors as its heat treat- 
ment, composition, and thickness and the wavelengths of the incident 
light. 

Louvers. Louvers are panels or baffles mounted in such a position that 
light transmitted by them is confined in a particular direction. They 
frequently are used to reduce the "spill" from a luminaire and thus to 
increase the attainable control. The most effective louvers have a small 
cross section (as viewed from the area to be lighted), are opaque, and have 
a flat black surface. However, louvers may be and often are translucent 
or finished in light colors. Typical louvers are shown in Fig. 7-18. 



LIGHT CONTROL 



7-15 



/ / / 



/ 



"71 



ANGLE OF EYE 
PROTECTION,/ 



/ / / . 
/ / / 



////////////// * 
////// /////// 



DEPTH OF 
LOUVER 



MORE SECTIONS 



LESS 
DEPTH 



PRINCIPLE OF LOUVER DESIGN 



CONTROL MAY BE IMPROVED BY USING MORE 
SHALLOW ONES OR THE SAME NUMBER 
OF GREATER DEPTH 




EGG CRATE DESIGN FOR 
FLUORESCENT LAMP FIXTURE 



STANDARD FOR 
INCANDESCENT-LAMP 
REFLECTOR 



SINGLE-LAMP 

CLIP-ON TYPE FOR 

FLUORESCENT LAMP 



FIG. 7-18. Typical louver designs. 



Polarization 

Light waves emitted by common sources are oriented at all angles in 
planes at right angles to the direction of the beam emitted from a source. 
As they pass through certain substances or are reflected from certain sur- 
faces at particular angles, vibrations in some directions are absorbed more 
than are those in other directions. Light which vibrates more strongly 
in certain directions is said to be polarized. 

The action of a taut rope fixed at one end and agitated at the other is 
analogous to that of a polarized light wave. As indicated in Fig. 7-19(a), 
when the end of the rope moves in a vertical line, a knot at any point along 
the rope will move in a parallel line. When the end of the rope moves 
through a circle, the knot will traverse a circle; and if the end revolves in 



PLANE 



NO MOTION TRANSMITTED^ 
MOTION STOPS 



WAVE PROGRESSES 
(NO CHANGE) 





POLARIZED TRANS- 
MITTER AXIS PER- 
PENDICULAR TO 
PLANE OF POLAR- 
IZATION OF WAVE 

'-- PARALLEL TO PLANE OF 
POLARIZATION OF WAVE 



FIG. 7-19. (a) Wave motion shows various types of polarization. (6) Polarized 
transmitters pass only that component of polarized wave motion which has its axis 
parallel to their plane of polarization. 



7-16 



I E S LIGHTING HANDBOOK 



an elliptical path, so will the knot. The movement of the knot in each case 
is in a plane perpendicular to the direction of propagation of the wave. 

If a pair of plates pierced by narrow slots, through which the rope is 
threaded, is introduced, as in Fig. 7-19(6), and the slots are oriented at 
right angles to each other, a most important characteristic of a polarized 
wave is revealed: a polarized transmitting plate passes only that component 
of the incident wave that is parallel to its axis of polarization. A polarized 
light transmitter introduced in a light path will pass only those disturb- 
ance components in planes parallel to its axis of polarization. 1 ' 2 

Examples of polarization. Skylight, particularly from the section oppo- 
site the sun, is somewhat polarized. Light from any source specularly 
reflected from glossy surfaces, such as glass, glossy paint, varnish, bodies of 
water, and so forth, also is partially polarized in a plane parallel to the 
reflecting surface. A polarizing transmitting material mounted in sun 
glasses with the plane of polarization normal to that of the reflecting sur- 
face absorbs the polarized specular reflection, permitting only the com- 
ponent of the unpolarized light parallel to the plane of polarization to pass 
through. 

Desk luminaires emitting polarized light have been produced 7 and it 
has been suggested that the glare of automobile headlights may be re- 
duced by polarizing their beams and then viewing the oncoming polarized 
headlights through a polarizing screen. 8 A screen in front of the driver 
with its axis oriented at 90 degrees with the beam would absorb the direct 
light of the headlight beam but would permit viewing the road, since pol- 
arized light which falls on the road is depolarized by reflection. 

Spectral transmission and polarizing characteristics of two polarizers are 
given in Fig. 7-20. 

Polarization may occur when light is reflected. For certain angles of incidence, 
polarization by reflection at surfaces of transmitting mediums may be nearly com- 
plete. This may be explained as follows: 

In Fig. 7-21 nonpolarized radiation is incident on the glass at P. Since light is a 



<40 





4 


5T 


POLV 


\RIZA 


TION 


\ 
\ 
\ 

\ 






®, 


/ 

/ 








\ 
1 

\ 
1 






y 












b : 




tET 




;_■ ^ 






•"" 




TRAf 


-JSMITTANC 


;e 




-4) 















-1 1.00 



0.96 cc 



0.45 0.50 0.55 0.60 0.65 0.70 0.76 
WAVELENGTH IN MICRONS 



FIG. 7-20. Characteristics of commer- 
cial polarizers: (a) Early type comprised 
of iodo-quinine sulphate crystals im- 
bedded in a plastic (trade name: Polaroid 
J film), (b) Modern polyvinyl alcohol 
molecular polarizer (trade name: Polar- 
oid H film). 








POLARIZATION 
COMPONENT: 

f IN PLANE OF PAPER 

PERPENDICULAR TO 

PLANE OF PAPER 



FIG. 7-21. Polarization by re- 
flection at a glass-air surface is 
at a maximum when the sum of 
the angle of incidence i plus the 
angle of refraction r equals 90 
degrees. (See text.) 



LIGHT CONTROL 



7-17 



transverse wave motion the disturbance at each point along the path can be resolved 
into two rectangular components, perpendicular to and in the same plane of the 
paper, indicated respectively by the dots and arrows. At the point of contact some 
of the incident light will be reflected, some refracted, some absorbed; and some of 
that absorbed will be re-emitted in the reflected ray. Since the motion is transverse, 
if the angle between reflected and refracted rays is 90 degrees, none of the disturb- 
ance components parallel to the plane of incidence of the refracted rays can be re- 
emitted in the reflected ray, and only radiation polarized in a plane parallel to the 
surface is reflected. 

The polarizing angle (sometimes called Brewster's angle) at which polarization 
will be most nearly complete, occurs when the sum of the angles of incidence i and re- 
fraction r equals 90 degrees. It is determined by the relationship known as 
Brewster's law : 

»2 = tan i 
where 

n» = index of refraction for the reflecting medium 
% = angle of incidence 
At all other angles of incidence the reflected ray will include polarization components 
in other planes. Figure 7-8 shows the variation in reflectance which occurs at vari- 
ous angles of incidence for both polarized and nonpolarized light at an air-glass 
surface. 



Interference 

When two light waves come together at different phases of their vibra- 
tion, they combine to make up a single wave whose amplitude equals the 
sum of the amplitudes of the two. This interference phenomenon is 
utilized to increase luminous transmittance, 6 and for extreme^ accurate 
thickness measurements in machine shops. 2 Interference also is the cause 
of the diffraction pattern which is sometimes seen around a pin hole or at 
the edge of a shadow cast by the sharp edge of an opaque screen and of 
irridescence in bubbles, oil slicks and other thin films. 9 

Low reflectance films. These films are applied to surfaces to reduce 
reflectance, increase transmittance, and consequently improve contrast 
relationships. The effect of these films on the reflectance of single and 
multisurface optical systems is shown in Fig. 7-22. Films a quarter wave 
length thick with an index of refraction between that of the medium sur- 
rounding the glass and that of the glass are used. The hardest and most 
permanent films are those of magnesium fluoride condensed on the trans- 




4 8 12 16 

NUMBER OF SURFACES 









— . 

UNTREATED 
GLASS, Rg 














INDEX OF 

REFRACTION 

FILM,n F =1.34 

GLASS 06=1.57 


















FILMED GLASS, 
R 























0.45 0.50 0.55 0.60 0.65 0.70 
WAVELENGTH IN MICRONS 



0.76 



FIG. 7-22. Reduction in reflection'losses by low reflection films. 



7-18 I E S LIGHTING HANDBOOK f 

mitting surface after thermal evaporation in vacuum, and protected by a 
thin layer of zircon or quartz applied in the same manner. 10 

The normal, uncoated, 4-per-cent reflection at air-glass surfaces may be 
reduced to less than 1 per cent at each filmed surface. This reduction is 
the result of cancelling interference between the waves reflected at the 
air — * film and film — » glass surfaces. 

Diffraction 

When a wave front is obstructed partially, as by the edge of a reflector 
or a louver, the shadow cast by the reflector or louver may be sharp or 
"soft," depending on the geometrical relationship and size of the source, 
reflector, and illuminated surface. This phenomenon, which is seldom of 
any consequence in ordinary lighting, is known as diffraction. 1 ' 2 

Diffusion 

Diffusion is the breaking up of a beam of light and the spreading of its 
rays in man}' directions by irregular reflection from microscopic foreign 
particles within a transmitting medium, or from microscopic irregularities 
of a reflecting surface. One almost perfectly diffuse reflecting surface is a 
freshly-cut, magnesium-oxide surface. Opal glass also is a good diffusor, 
when etched on one side. Perfect diffusion seldom is attained in practice 
but sometimes is assumed in calculations in order to simplify the math- 
ematics. 

Absorption 

Absorption occurs when a light beam enters a smoky atmosphere, or a 
piece of glass or plastic or meets a dense body. Part of the incident light 
is reflected from particle to particle within the body until its energy has 
been absorbed and converted into heat. Because of the nonuniform size 
of the particles (relative to the wavelength of light) and because of their 
spectral reflectance, the absorption characteristics of practically all mate- 
rials are selective (accompanied by change of color of light). 

REFERENCES 

1. Monk, G. S., Light Principles and Experiments, McGraw-Hill Book Co., Inc., New York, 1937. 

2. Hardy, A. C., and Perrin, F. H., The Principles of Optics, McGraw-Hill Book Co., Inc., New York, 1932. 

3. Franklin, William S., and Grantham, G. E-., General Physics, Franklin & Charles, Lancaster, Pa., 1930. 

4. Jolley, L. B. W., Waldram, J. M., and Wilson, G. H., The Theory and Design of Illuminating Engineering 
Equipment, Chapman & Hall, Ltd., London, 1930. 

5. Potter, W. M., "Some Notes on the Utilization of Internal Reflections," Ilium. Eng., March, 1945. 

6. Jacobs, D. H., Fundamentals of Optical Engineering, McGraw-Hill Book Co., Inc., New York, 1943. 

7. "New Polaroid Study Lamp," J. Optical Soc Am., September, 1940. Polarized Light and Its Ap- 
plication, Polaroid Corp., Cambridge, Mass., 1945. 

8. Roper, V., and Scott, K. D., "Seeing with Polarized Headlamps," Ilium. Eng., December, 1941. 
Chubb, L. W., "Polarized Light for Motor Vehicle Lighting," Trans. Ilium. Eng. Soc, May, 1937. Land, 
E. H., "Polaroid and the Headlight Problem," J. Franklin Inst., 1937. 

9. Dunning, J. R., and Paxton, H. C, Matter Energy and Radiation, McGraw-Hill Book Co., Inc., New 
York, 1941. 

10. Lyons, D. A., "Practical Applications of Metallic and Non-Metallic Film on Optical Elements," J. 
Optical Soc. Am., February, 1945. Jones F. L., and Homer, H. J., '"Chemical Methods of Increasing the 
Transparency of Glass," J. Optical Soc. Am., January, 1941. Cartwright, C. H., and Turner, A. F., U. S. 
Patent 2207656. Blodgett, K., "Use of Interference To Extinguish Reflection of Light from Glass," Phys. 
Rev., May, 1939. Kollmorgen, F., "Light Transmission Through Telescopes," Trans. Ilium. Eng. Soc, Feb- 
ruary, 1916. 



SECTION 8 
LIGHTING CALCULATIONS 

Engineering work in lighting as in all other fields requires the application 
of mathematical or graphical techniques to the solution of many different 
types of problems. 

At best, cut-and-try methods are inefficient. Often they are inaccurate 
and expensive. They are not likely to provide the best practical solution 
of even the most simple problem. 

Fortunately, it is possible to solve most lighting application problems 
without using anything more complicated than addition, subtraction, multi- 
plication, or division. Frequently, some of these operations may be 
avoided, if it is so desired, by using simple graphs and tables. A number 
of these time-saving short cuts are included in this section or in the Appen- 
dix, and others will be found in the references. It usually is necessary to 
compromise with accuracy to a certain extent when short-cut methods are 
used and this should be considered when choosing a method for solving a 
problem. In many cases, however, the short cuts save a great deal of time 
and provide reasonably accurate results. 

In addition to the methods of solving application problems given in this 
section, assistance in the solution of design and development problems will 
be found in the references at the end of the section and in the reference 
division. 

AVERAGE ILLUMINATION 

Many present-day interior lighting designs have as their major objective 
the provision of a certain average maintained general illumination level. 
Appendix Table A-l, page A-l, includes illumination levels (footcandles) 
representative of good practice in many commercial, industrial, educational, 
recreational, and home areas. 1 

The Lumen Method 

The method of calculation most frequently used to estimate the number 
and type of lamps or luminaires, or both, which will maintain a given aver- 
age illumination level in service in a particular interior is based on the 
classic experiments of Harrison and Anderson 2 who established a rela- 
tionship between the candlepower distribution characteristics of luminaires, 
their mounting height, and the room proportions. 

'-The required number of lamps of a particular type will equal the total 
initial light flux F divided by the rated lumen output of that type. 

- The required rated lumen output per lamp, when the number of lamps is 
fixed by the desired spacing, type of fixtures, or other consideration, will 
eoual the total initial light flux F divided by the number of lamps. 

Note: References are listed at the end of each section. 



8-2 I E S LIGHTING HANDBOOK 

The relationship may be expressed as the coefficient of utilization, A- u , 
in the following equations: 

7-7 * X "u X K m 7 _ fcj<xv X A. 

av A " u rTTT~7 

A F X k m 

= E av X A E av X A 

u X k m m = ~~ F X ku 

• » 

where E av = average illumination maintained in serv- 

ice on a horizontal working plane 30 
inches above the floor.* See Table 8-1. 

F — total initial light flux from all lamps 
(lumens) 

k u = coefficient of utilization (a dimension- 
less ratio) 

km — maintenance factor which compensates 
for the in-service reduction in light out- 
put of lamps and reflecting surface 
(dimensionless ratio) 

A = floor area (square feet) 

* Four per cent less than the absolute illumination. Corresponds approximately with reading of photome 
ter in which test plate error causes readings that are 4 per cent low. 

Values obtained using these equations are tabulated in Table 8-1 for various 
values of k u , k n , and A corresponding to a value of F = 1,000 lumens. 
Maintenance factor. Allowance must always lbe made for depreciation of 
lamps and light control elements below initia or design values so that 
the desired footcandle levels may be maintained in service. 3 For the most 
part, filament lamps average in service around 90 per cent of their initial 
lumen output and fluorescent lamps average around 80 per cent. Dust, 
grease, and so forth that collect quickly on reflecting surfaces account for 
another 10 to 20 per cent normal depreciation even with a reasonable clean- 
ing schedule. Therefore, the average illumination maintained in service 
will, under good conditions, be of the order of 60 to 70 per cent of the initial 
value, or 0.6-0.7 expressed as the maintenance factor, k m . In some in- 
stances, particularly with direct-lighting luminaires where there is little 
dust and smoke in the atmosphere, a higher value may be obtained. For 
open indirect equipment, cove lighting, skylights, and similar types of 
hard-to-reach and likely-to-be-neglected installations, a considerably lower 
factor should be assumed as indicated in Table 8-2. This table includes 
factors for these three conditions: 4 

1. Good maintenance factor — where the atmosphere is free of smoke, 
dust, and so forth, the luminaires are cleaned frequently, and the lamps are 
replaced systematically. 

2. Medium maintenance factor — where less clean atmospheric conditions 
exist, the luminaire cleaning is fair, and the lamps are replaced only after 
burnout. 

3. Poor maintenance factor — where the atmosphere is quite dirty and 
the equipment is poorly maintained. 



LIGHTING CALCULATIONS 



8-3 



Table 8-1. Average Maintained Illumination Produced on the Hori- 
zontal Working Plane per 1,000 Lamp Lumens* for Various 
Spacingf, Maintenance, and Utilization Conditions. 20 



A RE Af 
PER 
LAMP 


MAIN- 
TEN- 
ANCE 
FAC- 
TOR 


COEFFICIENT OF UTILIZATION 


(SQ FT) 


0.36 

25.2 
21.6 
18.0 


0.38 

26.6 
22.8 
19.0 


0.40 


0.42 

29.4 
25.2 
21.0 


0.44 

30.8 
26.4 
22.0 


0.46 

32.2 
27.6 
23.0 


0.48 

33.6 
28.8 
24.0 


0.50 

35.0 
30.0 
25.0 


0.52 

36.4 
31.2 
26.0 


0.54 

37.8 
32.4 
27.0 


0.56 

39.2 
33.6 
28.0 


0.58 

40.6 
34.8 
29.0 


0.60 

42.0 
36.0 
30.0 


0.62 

43.4 
37.2 
31.0 


0.64 

44.8 
38.4 
32.0 


0.66 

46.2 
39.6 
33.0 


0.68 

47.6 
40.8 
34.0 


0.70 


10 


70 
60 
50 


28.0 
24.0 
20.0 


49.0 
42.0 
35.0 


12 


70 
60 
50 


21.0 
18.0 
15.0 


22.1 
19.0 
15.8 


23.3 
20.0 
16.6 


24.5 
21.0 
17.5 


25.6 
22.0 
18.3 


26.8 
23.0 
19.2 


28.0 
24.0 
20.0 


29.1 
25.0 
20.8 


30.3 
26.0 
21.6 


31.5 

27.0 
22.5 


32.6 
28.0 
23.3 


33.8 
29.0 
24.1 


35.0 
30.0 
25.0 


36.1 
31.0 

25.8 


37.3 
32.0 
26.6 


38.5 
33.0 
27.5 


39.6 
34.0 

28.3 


40.8 
35.0 
29.1 


14 


70 
60 
50 


18.0 
15.4 
12.8 


19.0 
16.2 
13.5 


20.0 
17.1 
14.2 


21.0 
18.0 
15.0 


22.0 
18.8 
15.7 


23.0 
19.7 
16.4 


24.0 
20.5 
17.1 


25.0 
21.4 
17.8 


26.0 
22.2 
18.5 


27.0 
23.1 
19.2 


28.0 
24.0 
20.0 


29.0 
24.8 
20.7 


30.0 
25.7 
21.4 


31.0 
26.5 
22.1 


32.0 
27.4 
22.8 


33.0 
28.2 
23.5 


34.0 
29.1 
24.2 


35.0 
30.0 
25.0 


16 


70 
60 
50 


15.7 
13.5 
11.2 


16.6 
14.2 
11.8 


17.5 
15.0 
12.5 


18.3 
15.7 
13.1 


19.2 
16.5 
13.7 


20.1 
17.2 
14.3 


21.0 
18.0 
15.0 


21.8 
18.7 
15.6 


22.7 
19.5 
16.2 


23.6 
20.2 
16.8 


24.5 
21.0 
17.5 


25.3 
21.7 
18.1 


26.2 
22.5 

18.7 


27.1 
23.2 
19.3 


28.0 
24.0 
20.0 


28.8 
24.7 
20.6 


29.7 
25.5 
21.2 


30.6 
26.2 
21.8 


18 


70 
60 ■ 
50 


14.0 
12.0 
10.0 


14.7 
12.6 
10.5 


15.5 
13.3 
11.1 


16.3 
14.0 
11.6 


17.1 
14.6 
12.2 


17.8 
15.3 
12.7 


18.6 
16.0 
13.3 


19.4 
16.6 
13.8 


20.2 
17.3 
14.4 


21.0 
18.0 
15.0 


21.7 
18.6 
15.5 


22.5 
19.3 
16.1 


23.3 
20.0 
16.6 


24.1 
20.6 
17.2 


24.8 
21.3 
17.7 


25.6 
22.0 
18.3 


26.4 
22.6 
18.8 


27.2 
23.3 
19.4 


20 


70 
60 
50 


12.6 
10.8 
9.00 


13.3 
11.4 
9.50 


14.0 
12.0 
10.0 


14.7 
12.6 
10.5 


15.4 
13.2 
11.0 


16.1 
13.8 
11.5 


16.8 
14.4 
12.0 


17.5 
15.0 
12.5 


18.2 
15.6 
13.0 


18.9 
16.2 
13.5 


19.6 
16.8 
14.0 


20.3 
17.4 
14.5 


21.0 
18.0 
15.0 


21.7 
18.6 
15.5 


22.4 
19.2 
16.0 


23.1 
19.8 
16.5 


23.8 
20.4 
17.0 


24.5 
21.0 

17.5 


30 


70 
60 
50 


8.40 
7.20 
6.00 


8.86 
7.60 
6.33 


9.32 
8.00 
6.66 


9.80 
8.40 
7.00 


10.0 
8.80 
7.33 


10.7 
9.20 
7.66 


11.2 
9.60 
8.00 


11.6 
10.0 
8.33 


12.1 
10.4 
8.66 


12.6 
10.8 
9.00 


13.0 
11.2 
9.33 


13.5 
11.6 
9.66 


14.0 
12.0 
10.0 


14.4 
12.4 
10.3 


14.9 
12.8 
10.6 


15.4 
13.2 
11.0 


15.8 
13.6 
11.3 


16.3 
14.0 
11.6 


40 


70 
60 
50 


6.30 
5.40 
4.50 


6.65 
5.70 
4.75 


7.00 
6.00 
5.00 


7.30 
6.30 
5.25 


7.70 
6.60 
5.50 


8.05 
6.90 
5.75 


8.40 
7.20 
6.00 


8.75 
7.50 
6.25 


9.10 
7.80 
6.50 


9.45 
8.10 
6.75 


9.80 
8.40 
7.00 


10.1 
8.70 
7.25 


10.5 
9.00 
7.50 


10.8 
9.30 
7.75 


11.2 
9.60 
8.00 


11.5 
9.90 
8.25 


11.9 
10.2 
8.50 


12.2 
10.5 

8.75 


50 


70 
60 
50 


5.02 
4.32 
3.60 


5.32 
4.56 
3.80 


5.60 
4.80 
4.00 


5.88 
5.04 
4.20 


6.16 
5.28 
4.40 


6.44 
5.52 
4.60 


6.72 
5.76 
4.80 


7.00 
6.00 
5.00 


7.28 
6.24 
5.20 


7.56 
6.48 
5.40 


7.84 
6.72 
5.60 


8.12 
6.96 
5.80 


S.40 
7.20 
6.00 


8.6S 
7.44 
6.20 


8.96 
7.68 
6.40 


9.24 
7.92 
6.60 


9.52 
8.16 
6.80 


9.80 
8.40 
7.00 


60 


70 

60 
50 


4.20 
3.60 
3.00 


4.43 
3.80 
3.16 


4.66 
4.00 
3.33 


4.90 
4.20 
3.50 


5.13 
4.40 
3.66 


5.36 
4.60 
3.83 


5.60 
4.80 
4.00 


5.83 
5.00 
4.16 


6.06 
5.20 
4.33 


6.30 
5.40 
4.50 


6.53 
5.60 
4.66 


6.76 
5.80 
4.83 


7.00 
6.00 
5.00 


7.23 
6.20 
5.16 


7.46 
6.40 
5.33 


7.70 
6.60 
5.50 


7.93 
6.80 
5.66 


8.16 
7.00 
5.83 


70 


70 
60 
50 


3.60 
3.08 
2.57 


3.80 
3.25 

2.71 


4.00 
3.43 
2.85 


4.20 
3.60 
3.00 


4.40 
3.77 
3.14 


4.60 
3.94 
3.28 


4. SO 
4.11 
3.43 


5.00 
4.28 
3.57 


5.20 
4.45 
3.71 


5.40 
4.63 
3.85 


5.60 
4.80 
4.00 


5.80 
4.97 
4.14 


6.00 
5.14 

4.28 

5.25 
4.50 
3.75 


6.20 
5.31 
4.43 

5.42 
4.65 
3.87 


6.40 
5.48 
4.57 

5.60 
4.80 
4.00 


6.60 
5.66 
4.71 

5.77 
4.95 
4.12 


6.80 
5.83 
4.85 

5.95 
5.10 
4.25 


7.00 
6.00 
5.00 


80 


70 
60 
50 


3.15 
2.70 
2.25 


3.34 
2.85 
2.37 


3.50 
3.00 
2.50 


3.67 
3.15 
2.62 


3.85 
3.30 
2.75 


4.02 
3.45 

2.87 


4.20 
3.60 
3.00 


4.37 
3.75 
3.12 


4.55 
3.90 
3.25 


4.72 
4.05 
3.37 


4.90 
4.20 
3.50 


5.07 
4.35 
3.62 


6.12 
5.25 
4.37 


90 


70 
60 
50 


2.80 
2.40 
2.00 


2.95 
2.53 
2.11 


3.12 
2.66 
2.22 


3.26 
2.80 
2.33 


3.42 
2.93 
2.44 


3.57 
3.06 
2.55 


3.73 
3.20 
2.66 


3.88 
3.13 

2.77 


4.04 
3.46 

2.88 


4.20 
3.60 
3.00 


4.35 
3.73 
3.11 


4.51 
3.86 
3.22 


4.66 
4.00 
3.33 


4.82 
4.13 
3.44 


4.97 
4.26 
3.55 


5.13 
4.40 
3.66 


5.2S 
4.53 
3.77 


5.44 
4.66 
3.S8 


100 


70 

60 
50 


2.52 
2.16 
1.80 


2.66 
2.28 
1.90 


2.80 
2.40 
2.00 


2.94 
2.52 
2.10 


3. OS 
2.64 
2.20 


3.22 
2.76 
2.30 


3.36 
2.88 
2.40 


3.50 
3.00 
2.50 


3.64 
3.12 
2.60 


3.78 
3.24 
2.70 


3.92 
3.36 
2.80 


4.06 
3.48 
2.90 


4.20 
3.60 
3.00 


4.34 
3.72 
3.10 


4.4S 
3.84 
3.20 


4.62 
3.96 
3.30 


4.76 
4.08 
3.40 


4.90 
4.20 
3.50 


150 


70 

60 
50 


1.68 
1.44 
1.20 


1.77 
1.52 
1.26 


1.86 
1.60 
1.33 


1.96 
1.68 
1.40 


2.05 
1.76 
1.46 


2.14 
1.84 
1.53 


2.24 
1.90 
1.60 


2.33 
1.98 
1.66 


2.42 
2.06 
1.73 


2.52 
2.14 
1.80 


2.61 
2.22 
1.86 


2.70 
2.30 
1.93 


2.80 
2.38 
2.00 


2.89 
2.46 
2.06 


2.98 
2.54 
2.13 


3.08 
2.62 
2.20 


3.17 
2.70 
2.26 


3.26 
2.78 
2.33 


200 


70 
60 
50 


1.26 
1.08 
.900 


1.33 
1.14 
.950 


1.40 
1.20 
1.00 


1.47 1.54 
1.26 1.32 
1.05 1.10 


1.61 
1.38 
1.15 


1.6S 
1.44 
1.20 


1.75 
1.50 
1.25 


1.82 
1.56 
1.3C 


1.89 
1.62 
1.35 


1.96 
1.68 
1.40 


2.03 
1.74 
1.45 


2.10 
1.80 
1.50 


2.17 
1.86 
1.55 


2.24 
1.92 
1.60 


2.31 
1.98 
1.65 


2.38 
2.04 
1.70 


2.45 
2.10 
1.75 



* If lamp output is 2,000 lumens multiply tabulated values by jh^rk- 

500 
If lamp output is 500 lumens multiply tabulated values by 7755,. Table applies to all types of lamps. 

t If area per luminaire or per room rather than area per lamp is used, divide tabulated values by no. of 
lamps per luminaire or no. of lamps per room respectively. 



Table 8-2. Coefficients of Utilization, Efficiencies,* Distribution Character- 
istics,! and Maintenance Factors! for Typical Luminaires Computed for 
a Wide Range of Installation Conditions. § 4 









Ceiling . . . 




70% 






50% 




30% 




525 


SPACING 


















LUMINAIRE 


Q 


and Main- 
tenance 
Factor 


Walls 


50% 


30% 


10% 


50% 


30% 


10% 


30% | 10% 




Room 
Index 


COEFFICIENT OF UTILIZATION 


Spacing not 
» to exceed 


J 


.37 


.31 


.27 


.36 


.31 


.27 


.31 


.27 




I 


.45 


.41 


.38 


.45 


.40 


.37 


.40 


.37 


H 


.49 


.45 


.42 


.49 


.45 


.42 


.45 


.42 


^3^1^ T 


G 


.53 


.49 


.46 


.53 


.49 


.46 


.48 


.46 


F 
E 
D 


.56 
.61 
.66 


.53 
.58 
.63 


.49 
.55 
.60 


.55 
.60 

.64 


.52 

.57 
.62 


.49 
.55 
.60 


.51 
.56 
.61 


.49 
.55 
.60 


MF 


G .75 


C 


.67 


.65 


.62 


.66 


.64 


.62 


.63 


.61 


Direct: R.L.M. Dome M .65 


B 


.71 


.68 


.66 


.69 


.67 


.65 


.66 


.64 


Reflector P .55 


A 


.72 


.70 


.67 


.71 


.68 


.67 


.67 


.66 


Spacing not 


J 


.35 


.31 


.28 


.34 


.31 


.28 


.30 


.28 


JfL ; " Mu 


I 


.43 


.39 


.37 


.42 


.39 


.37 


.39 


.37 


H 


.46 


.44 


.42 


.46 


.44 


.42 


.43 


.42 


G 


.50 


.47 


.45 


.49 


.47 


.45 


.46 


.45 


ml /llmffiii 1 


F 


.53 


.50 


.47 


.51 


.49 


.47 


.49 


.47 


4K____^ 


E 


.56 


.54 


.51 


.56 


.54 


.11 


.53 


.51 


MF 


D 


.61 


.58 


.56 


.59 


.57 


.(6 


.56 


.56 


G .75 


C 


.62 


.60 


.57 


.61 


.58 


.57 


.58 


.56 


Direct: R.L.M. Deep-Bowl ]\j 55 


B 


.64 


.62 


.61 


.63 


.61 


.60 


.60 


.59 


Reflector P .55 


A 


.65 


.63 


.61 


.64 


.62 


.61 


.61 


.60 


Spacing not 


















to exceed 


J 


.43 


.40 


.39 


.42 


.40 


.39 


.40 


.38 


J-3L 0.6 xMH 


I 


.51 


.50 


.49 


.50 


.49 


.48 


.49 


.46 




H 


.55 


.54 


.53 


.54 


.53 


.52 


.53 


.52 


(III ui\ ! 


G 


.59 


.58 


.57 


.58 


.56 


.55 


.56 


.55 


C_j T 


F 


.61 


.60 


.58 


.59 


.58 


.58 


.58 


.57 


E 


.64 


.63 


.62 


.63 


.62 


.61 


.61 


.60 


75 MF 


D 


.68 


.65 


.64 


.66 


.65 


.64 


.64 


.63 


Direct: Aluminum High-Bay G» .75 


C 


.69 


.67 


.65 


.67 


.66 


.64 


.64 


.64 


Reflector, Concentrating M .60 

P .40 


B 
A 


.70 

.71 


.68 
.70 


.67 
.68 


.68 
.69 


.67 

.67 


.66 
.67 


.66 
.67 


.65 
.66 


Spacing not 
^\ to exceed 


J 


.40 


.36 


.34 


.39 


.36 


.34 


.36 


.33 




I 


.48 


.45 


.43 


.47 


.44 


.43 


.44 


.42 


/<^v ° 1 x MH 


H 


.52 


.50 


.48 


.51 


.49 


.47 


.49 


.47 


G 


.55 


.53 


.52 


.55 


.52 


.51 


.52 


.51 


//// llili T 


F 


.58 


.56 


.53 


.56 


.55 


.53 


.55 


.53 


emjr ~^s& 


E 


.62 


.60 


.58 


.61 


.59 


.57 


.58 


.57 


75 MF 


D 


.66 


.63 


.61 


.64 


.62 


.61 


.62 


.61 


G .75 


C 


.67 


.65 


.62 


.66 


.64 


.62 


.63 


.62 


Direct: Aluminum High-Bay M .65 


B 


.69 


.67 


.66 


.67 


.65 


.64 


.65 


.64 


Reflector, Medium Spread P .50 


A 


.70 


.68 


.67 


.69 


.67 


.65 


.66 


.64 



* per cent of initial lamp lumens in upper hemisphere. + 79 = initial luminaire efficiency. 

Jl 

1 

79 79 per cent of initial lamp lumens in lower hemisphere, 
t I.C.I classifications: D = direct; SB = semidirect; G = general diffuse; SI = semi-indirect; I = indirect . 
j MF = Maintenance factors based on the following percentages of initial lamp lumens emitted at 70-per- 
cent rated life: 40-watt fluorescent 0.76, 100-watt fluorescent 0.72, incandescent 0.85, mercury 0.S4. 
G = Good. M = Medium. P = Poor. 
Note: Consider cleaning schedule, ceiling and wall reflectances, type of work, heating, and ventilation as 
well as type of lamp and luminaire when choosing factor. Good conditions are seldom encountered. 
§ MH = Mounting height above floor. 

CH = Ceiling height above floor. 
Room indices for rooms of different proportions are given in Table 8-3. 



LIGHTING CALCULATIONS 



8-5 



Table 8-2. Continued 









Ceiling.. . 




70% 






50% 




30% 




£ 


SPACING 
and Main- 
tenance 
Factor 
















LUM1NAIRE 




Walls 


50% 


30% 


10% 


50% 


30% 


10% 


30% | 10% 




Room 
Index 


COEFFICIENT OF UTILIZATION 


Spacing not 


J 


.40 


.38 


.36 


.39 


.38 


.36 


.38 


.36 


ex ee 


I 


.48 


.46 


.45 


.47 


.46 


.45 


.45 


.43 


ft o Cone. 


H 


.52 


.51 


.50 


.51 


.50 


.49 


.50 


.48 


ZmL, I °'Med IH 


G 


.55 


.54 


.53 


.54 


.53 


.52 


.53 


.51 


F 


.57 


.56 


.55 


.56 


.55 


.54 


.55 


.53 


jtfi^^Tj^ i . 8 x M U 


E 


.b0 


.59 


.58 


.59 


.58 


.57 


.57 


.56 


^■"-"^-""^ 70 MF 


D 


.64 


.61 


.60 


.62 


.60 


.59 


.60 


.59 


C 80 
Direct: Concentrating or ]yj '72 


C 


.64 


.63 


.61 


.63 


.62 


.60 


.60 


.60 


B 


.65 


.64 


.63 


.64 


.63 


.62 


.62 


.61 


Medium, Heavy-Duty Type p '^ 


A 


.66 


.65 


.64 


.64 


.63 


.62 


.62 


.62 


Spacing not 


J 


.37 


.34 


.31 


.36 


.34 


.31 


.34 


.31 


^ to exceed 


I 


.45 


.42 


.41 


.44 


.41 


.40 


.41 


.39 


B ° 1 . 1 x MH 


H 


.48 


.46 


.45 


.49 


.45 


.44 


.45 


.44 


//Mmk. ^ 


G 


.52 


.50 


.48 


.51 


.49 


.48 


.49 


.48 


if/Hrai ~ 


F 


.55 


.52 


.51 


.54 


.51 


.50 


.51 


.50 


JiPhL 1 


E 


.57 


.56 


.54 


.57 


.55 


.53 


.55 


.53 


**^^ m -f*~& 70 ]\jp 


D 


.62 


.59 


.57 


.60 


.58 


.57 


.57 


.56 


G 80 


C 


.63 


.61 


.58 


.62 


.59 


.58 


.59 


.58 


Direct: Wide Spread, M 72 


B 


.64 


.62 


.61 


.63 


.61 


.60 


.60 


.59 


Heavy -Duty Type p ^5 


A 


.66 


.64 


.62 


.64 


.62 


.61 


.62 


.60 


Spacing not 


J 


.27 


..23 


.20 


.26 


.23 


.20 


.22 


.20 


to exceed 


I 


.34 


.30 


.28 


.33 


.29 


.27 


.29 


.27 


(■I six MH 


H 


.37 


.34 


.31 


.36 


.33 


.31 


.32 


.30 


^sL 1 


G 


.40 


.37 


.34 


.39 


.36 


.34 


.35 


.33 


F 


.42 


.39 


.37 


.40 


.38 


.36 


.37 


.36 


/ lllli rx\. 


1 

« MF 


E 
D 


.46 
.49 


.43 

.47 


.41 
.44 


.45 
.48 


.42 
.46 


.40 
.44 


.41 
.44 


.40 


«gvV-.„ _ Z3» 


.43 


" G .70 


C 


.51 


.49 


.46 


.49 


.47 


.46 


.46 


.44 


Direct: R.L.M. Glassteel M .60 


B 


.53 


.51 


.49 


.51 


.49 


.48 


.48 


.47 


Diffuser p - 45 


A 


.54 


.53 


.51 


.53 


.51 


.49 


.49 


.48 


Spacing not 
to exceed 


J 


.38 


.36 


.35 


.38 


.36 


.35 


.38 


.35 


I 


.46 


.45 


.44 


.45 


.44 


.43 


.44 


.42 


rjL 0.8 xMH 


II 


.49 


.49 


.48 


.49 


,48 


.47 


.48 


.47 


4r~^^ """^ ° 


G 


.53 


.52 


.51 


.52 


.51 


.50 


.51 


.49 


/^>C^T^~% t 


F 


.55 


.54 


.53 


.53 


.53 


.52 


.53 


.51 


x^-— </ * MF 


E 


.57 


.57 


.56 


.57 


.56 


.55 


.55 


.54 


D 


.61 


.59 


.58 


.59 


.58 


.57 


.57 


.56 


* 7 G .60 


C 


.62 


.61 


.59 


.60 


.59 


.58 


.58 


.57 


Direct: R.L.M. Silvered M -50 


B 


.63 


.62 


.61 


.61 


.60 


.59 


.59 


.58 


Bowl Diffuser P -40 


A 


.64 


.63 


.62 


.62 


.61 


.60 


.60 


.59 


Spacing not 
to exceed 


J 


.31 


.26 


.23 


.30 


.26 


.23 


.26 


.23 


I 


.38 


.34 


.31 


.37 


.33 


.31 


.33 


.31 


H 1 x MH 


H 


.41 


.38 


.34 


.41 


.38 


.34 


.37 


.34 


-^wf^^^ f 


G 


.45 


"'.41 


.39 


.44 


.41 


.39 


.40 


.39 


^52PHk\ — 


F 


.47 


.44 


.41 


.46 


.43 


.41 


.43 


.41 


^Z\^z_3 i 


E 


.51 


.48 


.46 


.50 


.48 


.46 


.47 


.46 


« MF 


D 


.55 


.52 


.50 


.54 


.52 


.50 


.51 


.50 


Direct : Wide Spread, -** ' fir - 


C 
B 


.56 
.59 


.54 
.57 


.52 
.55 


.55 

.58 


.53 

.56 


.52 

.54 


.52 
.55 


.51 
.54 


Vapor Tight p [55 


A 


.60 


.58 


.56 


.59 


.57 


.56 


.56 


.55 



8-6 



I E S LIGHTING HANDBOOK 









Table 8-2. Continued 




















Ceiling. . 




70% 






50% 




30% 




[5 


SPACING 
and Main- 
tenance 
F actor 


















LUMINAIRE 


Q 


Walls 


50% 


30% 


10% 


50% 


30% 


10% 


30% 


10% 




Room 
Index 


COEFFICIENT OF UTILIZATION 


Spacing not 
to exceed 


J 


.25 


.22 


.20 


.24 


.22 


.20 


.22 


.20 




^*»^ O.SxMH 


I 


.31 


.28 


.26 


.29 


.28 


.26 


.28 


.26 




H 


.34 


.31 


.29 


.32 


.31 


.29 


.30 


.28 




Jn t 


G 


.36 


.33 


.32 


.34 


.33 


.31 


.32 


.30 


J^^^-^^L 


F 


.38 


.35 


.34 


.36 


.34 


.33 


.34 


.32 


<^^»^-^^J> | 


E 


.40 


.39 


.38 


.39 


.37 


.36 


.37 


.35 


^<=^^ 33 MF 


D 


.43 


.41 


.40 


.42 


.40 


.39 


.39 


.38 


G .70 


C 


.45 


.43 


.42 


.44 


.41 


.40 


.40 


.40 


^- ^ , ™ M .60 

Direct: Enclosed Lens-BIate p 5Q 


B 
A 


.48 
.50 


.45 
.47 


.44 
.46 


.47 

.48 


.43 

.46 


.42 

.45 


.42 
.45 


.41 
.44 


Distributing Type 




















Spacing not 
to exceed 


J 


.38 


.32 


.28 


.37 


.32 


.28 


.31 


.28 


1 xMH 


I 


.47 


.42 


.39 


.46 


.41 


.38 


.40 


.37 


H 


.51 


.47 


.44 


.50 


.47 


.43 


.46 


.43 


^g^'N, ° 


G 


.55 


.51 


.48 


.54 


.51 


.47 


.50 


.47 


jg^^S^^jN t 


F 


.58 


.54 


.51 


.57 


.53 


.51 


.52 


.50 


^z^^^^^^g^^ ~ 


E 


.63 


.60 


.57 


.62 


.59 


.56 


.58 


.55 


^^t^^^^z*^^ ' ^F 


D 


.68 


.64 


.61 


.66 


.64 


.61 


.63 


.60 


^ %5 %^^* :ss: ^ 79 G .65 


C 


.70 


.67 


.63 


.68 


.65 


.64 


.64 


.62 


M .55 


B 


.73 


.70 


.68 


.71 


.68 


.67 


.67 


.66 


Direct: Two 40-Watt Lamps -4 ° 


A 


.74 


.72 


.70 


.72 


.70 


.68 


.69 


.67 


Spacing not 
to exceed 


J 


.34 


.29 


.25 


.33 


.29 


.25 


.28 


.25 


^T^ ° ! x MH 


I 


.42 


.38 


.35 


.41 


.37 


.34 


.37 


.34 


II 


.46 


.42 


.39 


.44 


.42 


.39 


.41 


.39 


^j^^^>^^\ | 


G 


.50 


.46 


.43 


.48 


.45 


.41 


.44 


.41 


^£^^^^>^^ — 


F 


.53 


.49 


.46 


.51 


.47 


.44 


.47 


.44 


^^^^^^^^^^^ \ 


E 


.57 


.54 


.51 


.56 


.52 


.50 


.52 


.50 


i^^^^^-s*** 1 ^ 72 MF 


D 


.61 


.58 


.55 


.59 


.56 


.54 


.56 


.54 


^ Ss * sS ^ G .65 


C 


.63 


.60 


.57 


.61 


.58 


.56 


.58 


.56 


Direct: Three 40-Watt p 1 ;Jjj 
Lamps 


B 

A 


.66 
.67 


.64 
.65 


.61 
.62 


.64 
.66 


.60 

.62 


.59 

.61 


.60 
.62 


.59 
.60 


Spacing not 
to exceed 


J 


.33 


.28 


.25 


.33 


.28 


.25 


.28 


.25 




I 


.41 


.37 


.34 


.40 


.36 


.33 


.36 


.33 


^r\ * x MH 


H 


.45 


.41 


.38 


.44 


.41 


.38 


.40 


.38 


^^0§%^^S\ \ 


G 


.48 


.45 


.42 


.48 


.45 


.42 


.43 


.42 


^£^z^Z^^^» — 


F 


.51 


.48 


.45 


.50 


.47 


.45 


.46 


.45 


*^&^^^^^^^^ | 


E 


.55 


.53 


.50 


.55 


.52 


.50 


.51 


.50 


^Vfc^^***^^ 71 MF 


D 


.60 


.57 


.54 


.58 


56 


.54 


.55 


.54 


G .60 


C 


.61 


.59 


.56 


.60 


.57 


.56 


.57 


.55 


Direct: Two 100-Watt £? 52 


B 


.64 


.62 


.60 


.62 


.60 


.59 


.60 


.58 


•"•* » » w ~ ~ • ■•- r 4- ^ 


A 


.65 


.63 


.61 


.64 


.62 


.60 


.61 


.60 


Lamps 




















Spacing not 
to exceed 


J 


.33 


.28 


.26 


.32 


.28 


.26 


.28 


.26 




I 


.39 


.36 


.34 


.39 


.35 


.34 


.35 


.34 


,^£^fe^\ jO.Px'.MH 


H 


.43 


.40 


.38 


.42 


.40 


.38 


.39 


.38 


^i^^^^^^^^^^Mt ~ 


G 


.46 


.43 


.41 


.45 


.43 


.41 


.42 


.41 


ij 1 ^^^^^^^^^ \ 


F 


.48 


.46 


.43 


.47 


.45 


.43 


.45 


.43 


^=^J~f^iS^^^ 


E 


.52 


.50 


.47 


.51 


.49 


.47 


.48 


.47 


^^^^ MF 


D 


.55 


.53 


.51 


.54 


.52 


.51 


.52 


.51 


^. .... , T G .65 


C 


.57 


.55 


.52 


.56 


.53 


.52 


.53 


.52 


Direct: With Louvers, ]yj 55 


B 


.59 


.57 


.56 


.57 


.56 


.55 


.55 


.54 


two 40-Watt lamps p '45 


A 


.60 


.58 


.56 


.59 


.57 


.56 


.56 


.55 



LIGHTING CALCULATIONS 



8-7 









Table 8-2. Continued 
















- 






Ceiling. . . 




70% 






50% 




30% 






tg 


SPACING 
and Main- 
tenance 
Factor 




















LUMINAIRE 


o 


Walls 


50% 


30% 


10% 


50% 


30% 


10% 


30% | 10% 




Room 
Index 


COEFFICIENT OF UTILIZATION 






Spacing not 


J 


.29 


.26 


.23 


.28 


.26 


.23 


.25 


.23 






to exceed 


I 


.35 


.32 


.31 


.35 


.32 


.30 


.32 


.30 




^_o^ o 


1 xMH 


H 


.38 


.36 


.34 


.38 


.36 


.34 


.35 


.34 




^^^-^~zjLy\ \ 




G 


.41 


.39 


.37 


.41 


.39 


.37 


.38 


.37 




^-*^^fG^^^^^Sg^!m* — 




F 


.44 


.41 


.39 


.42 


.41 


.39 


.40 


.39 




,£gifgjg§§^^^ s=S * ==== ** = ^ i 




E 


.46 


.45 


.42 


.46 


.44 


.42 


.44 


.42 




40 


MF 


D 


.50 


.48 


.46 


.49 


.47 


.46 


.46 


.46 






G .70 


C 


.51 


.49 


.47 


.50 


.48 


.47 


.48 


.46 




Direct: Vapor and Dust 
Tight, two or three 


M .65 
P .55 


B 
A 


.53 

.54 


.51 
.52 


.50 
.50 


.52 
.53 


.50 
.51 


.49 
.50 


.49 
.50 


.49 
.49 




40-watt Lamps 


Spacing not 














.28 


.31 






J 


.38 


.32 


.28 


.37 


.32 


.28 






to exceed 


I 


.47 


.42 


.39 


.46 


.41 


.38 


.41 


.38 




^ifiSSV ° 


1 xMH 


H 


.51 


.47 


.43 


.50 


.47 


.43 


.46 


.43 




^^0^) t 




G 


.55 


.51 


.47 


.54 


.51 


.47 


.49 


.47 




^^^^^ - 




F 


.58 


.54 


.51 


.56 


.53 


.51 


.52 


.51 




4m3- -^ \ 




E 


.63 


.59 


.56 


.62 


.59 


.56 


.58 


.56 




80 


MF 


D 


.67 


.64 


.61 


.66 


.63 


.61 


.63 


.61 




Direct: 


G .70 


C 


.69 


.67 


.64 


.67 


.65 


.63 


.64 


.63 




Three Kw Reflector, one 


M ^60 


B 


.72 


.70 


.67 


.71 


.68 


.67 


.67 


.66 




3,000-Watt Mercury Lamp 


P .50 

Spacing not 


A 


.74 


.71 


.69 


.72 


.70 


.68 
.35 


.69 
.37 


.67 




J 


.40 


.37 


.35 


.39 


.37 


.35 




-xs^^^ 


to exceed 


I 


.48 


.46 


.45 


.47 


.45 


.44 


.44 


.43 




^~^!^^v o 


O.SxMH 


H 


.52 


.50 


.50 


.51 


.49 


.49 


.48 


.48 




^S^^-^jL i 




G 


.55 


.54 


.53 


.54 


.53 


.51 


.51 


.50 




.^^>^^=^^ — 




F 


.58 


.56 


.54 


.55 


.54 


.53 


.53 


.52 




^^^^^^^^^ 1 




E 


.60 


.59 


.57 


.59 


.58 


.56 


.57 


.55 




^^^^^^^ 72 


MF 


D 


.65 


.62 


.60 


.62 


.61 


.59 


.59 


.58 




^^&=*^^ 


G .70 


C 


.66 


.64 


.61 


.64 


.62 


.61 


.61 


.60 






M .60 


B 


.67 


.65 


.64 


.65 


.63 


.62 


.62 


.61 




Direct: Troffer, Open Type 


P .55 

Spacing not 


A 


.68 


.66 


.65 
.25 


.66 

.32 


.65 

.28 


.63 
.25 


.64 

.28 


.62 


/ 


J 


.32 


.28 


.25 


^^^ ^^ 


to^exceed 


I 


.40 


.36 


.34 


.39 


.35 


.33 


.35 


.33 




^^^»qP*\ 


0.8xMH 


H 


.43 


.39 


.37 


.42 


.39 


.37 


.39 


.36 




-^gpE* - 




G 


.46 


.43 


.41 


.45 


.43 


.41 


.43 


.40 






F 


.48 


.45 


.43 


.47 


.45 


.43 


.45 


.42 




^^5^i^ x '^ i 




E 


.52 


.50 


.48 


.51 


.49 


.47 


.49 


.46 




ss^^t^^^^ 


MF 


D 


.56 


.54 


.52 


.55 


.53 


.51 


.53 


.50 




*^Zx^^ 


G .70 


C 


.57 


.55 


.53 


.56 


.54 


.52 


.54 


.51 






M .60 


B 


.60 


.58 


.56 


.59 


.57 


.55 


.56 


.54 




Direct: Troffer with Louvers 


P .55 

Spacing not 


A 


.61 


.59 


.57 


.60 

.29 


.58 
.26 


.57 
.23 


.57 
.26 


.56 




J 


.30 


.26 


.23 


.23 






to exceed 


I 


.37 


.33 


.31 


.36 


.32 


.30 


.32 


.30 




.^#jj^Jfc 


0.8xMH 


H 


.40 


.36 


.34 


.39 


.36 


.34 


.36 


.33 




^^SS^ | 




G 


.42 


.40 


.38 


.41 


.40 


.3S 


.40 


.37 






F 


.44 


.41 


.40 


.43 


.41 


.40 


.41 


.39 




^<0^^* s 




E 


.48 


.46 


.44 


.47 


.45 


.43 


.45 


.42 




MF 


D 


.52 


.50 


.48 


.51 


.49 


.47 


.49 


.46 




>«^Er25^^ 


G .70 


C 


.53 


.51 


.49 


.52 


.50 


.48 


.50 


.47 






M .60 


B 


.55 


.53 


.52 


.54 


.53 


.51 


.52 


.50 




Direct: Troffer with Loui 


fers 


P .55 


A 


.56 


.54 


.53 


.55 


.54 


.53 


.53 


.52 



8-8 



I E S LIGHTING HANDBOOK 







Table 8-2. Continued 
















£ 


SPACING 
and Main- 
tenance 
Factors 


Ceiling . . . 


70% 


50% 


30% 


LUMINAIRE 


Q 


Walls 


50% 


30% 


10% 


50% 


30% 


10% 


30% 1 10% 




Room 
Index 


COEFFICIENT OF UTILIZATION 


. -^ 


Spacing not 
to exceed 


J 


.28 


.24 


.22 


.27 


.24 


.22 


.24 


.22 


^^^&\ ° 


1 xMH 


I 


.34 


.31 


.29 


.33 


.30 


.29 


.30 


.29 


^^PSCJL t 


H 


.37 


.34 


.33 


.36 


.34 


.32 


.33 


.32 


^=^^jti|p^ — 




G 


.39 


.37 


.36 


.38 


.37 


.35 


.38 


.37 


^ ~J^^^ \ 




F 


.42 


.39 


.37 


.40 


.38 


.37 


.41 


.40 


ggz^^ j j 




E 


.44 


.43 


.40 


.43 


.42 


.40 


.42 


.41 


■"^^^^^ 


MF 


D 


.47 


.45 


.43 


.46 


.45 


.43 


.44 


.43 




G .70 


C 


.49 


.47 


.45 


.47 


.46 


.45 


.45 


.44 


Direct: Troffer with Ribbed- 
Glass Cover 


M .60 
P .50 

Spacing not 


B 
A 


.50 
.51 


.48 
.50 


.47 

.48 


.49 
.50 


.47 

.48 


.46 
.47 


.46 

.47 


.45 
.46 




J 


.29 


.26 


.23 


.28 


.26 


.23 


.25 


.23 


^^^A\ Fv^> ° 




I 


.35 


.32 


.31 


.35 


.32 


.30 


.32 


.30 


/^^p^M^J\ t 


1 x MH 


H 


.38 


.36 


.34 


.38 


.36 


.34 


.35 


.34 






G 


.41 


.39 


.37 


.41 


.39 


.37 


.38 


.37 


"^^^^^^^^ * 




F 


.44 


.41 


.39 


.42 


.41 


.39 


.40 


.39 


\^s*>&^ i ^ io 




E 


.46 


.45 


.42 


.46 


.44 


.42 


.44 


.42 




MF 


D 


.50 


.48 


.46 


.49 


.47 


.46 


.46 


.46 


Direct: With Louvers four 


G .70 


C 


.51 


.49 


.47 


.50 


.48 


.47 


.48 


.46 


40-Watt Lamps 


M .60 
P .55 

Spacing not 
to exceed 


B 
A 


.53 

.54 


.51 
.52 


.50 
.50 

.23 


.52 

.53 

.32 


.50 
.51 

.26 


.49 

.50 

.23 


.49 
.50 

.25 


.49 
.49 




J 


.32 


.27 


.23 


9 


I 


.40 


.35 


.31 


.39 


.34 


.30 


.34 


.30 




1 x MH 


H 


.44 


.39 


.36 


.43 


.39 


.35 


.36 


.35 




G 


.48 


.43 


.40 


.46 


.42 


.39 


.41 


.39 


^'^^^ ""^j^T T 




F 


.52 


.47 


.43 


.50 


.46 


.42 


.45 


.42 


T^ 




E 


.57 


.52 


.48 


.55 


.51 


.47 


.50 


.46 


" 77 


MF 


D 


.62 


.56 


.52 


.59 


.55 


.51 


.54 


.51 


Direct: Bare Lamp with 
White Reflecting Surface 


G .75 
M .65 
P .55 

Spacing not 
to exceed 


C 
B 
A 


.65 
.69 
.71 


.59 
.63 
.66 


.54 
.59 
.62 


.62 
.65 
.67 


.57 
.61 
.63 


.54 
.58 
.60 


.56 
.60 
.61 


.53 
.58 
.60 




J 


.23 


.19 


.17 


.23 


.18 


.16 


.17 


.16 


18 


I 


.29 


.25 


.22 


.28 


.24 


.21 


.23 


.21 


-=^§iiSft^. t 


1 x MH 


H 


.32 


.28 


.25 


.31 


.28 


.25 


.26 


.24 


-*ss^^§^^§§5§aJ _ 




G 


.36 


.32 


.29 


.34 


.30 


.27 


.29 


.26 


^^^00^^B^~3&*r \ 




F 


.40 


.35 


.31 


.37 


.33 


.30 


.31 


.29 


v2£-^^^ = '"^^ ==== J3 




E 


.43 


.39 


.35 


.41 


.37 


.34 


.35 


.32 




MF 


D 


.47 


.42 


.39 


.44 


.40 


.37 


.38 


.36 




G .75 


C 


.49 


.45 


.41 


.46 


.42 


.39 


.40 


.38 


Semidirect: Glass-Enclosed 


M .65 


B 


.52 


.48 


.45 


.49 


.45 


.43 


.43 


.41 


one 40-watt Lamp 


P .55 

Spacing not 


A 


.54 


.51 


.47 


.51 


.47 


.45 


.44 


.43 




J 


.24 


.20 


.19 


.23 


.20 


.17 


.19 


.17 




to exceed 


I 


.30 


.26 


.23 


.29 


.25 


.23 


.25 


.23 


^^^. 9 


1 x MH 


H 


.33 


.29 


.27 


.32 


.29 


.26 


.28 


.26 


^-^SS^SS?^^) \ 




G 


.36 


.32 


.30 


.34 


.32 


.29 


.30 


.29 


^^^^s^P^filiiPw ~ 




F 


.39 


.35 


.32 


.37 


.34 


.31 


.33 


.31 


f^5JJ^§jgf§§£J^ \ 




E 


.42 


.39 


.35 


.41 


.38 


.35 


.36 


.34 


T^r^^^^ 3 ^*^ J, 


MF 


D 


.45 


.42 


.39 


.44 


.41 


.38 


.40 


.38 




G .75 


C 


.47 


.44 


.41 


.45 


.42 


.40 


.41 


.39 


Semidirect: Glass-Enclosed 


M .65 


B 


.50 


.47 


.44 


.48 


.45 


.43 


.44 


.42 


two 40-Watt Lamps 




P .55 


A 


.52 


.49 


.46 


.50 


.47 


.45 


.45 


.44 



LIGHTING CALCULATIONS 



8-9 



Table 8-2. Continued 





£ 




Ceiling . . . 


70% 


50% 


30% 






SPACING 


















LUMINAIRE 


iJ,0 
Q 


and Main- 
tenance 
Factor 


Walls 


50% | 


30% | 


10% 1 


50% 


30% | 


10% 


30% | 10% 




Room 
Index 


COEFFICIENT OF UTILIZATION 


Spacing not 
to exceed 


J 


.21 


.17 


.14 


.20 


.16 


.14 


.16 


.14 


^=r^ s 1 x MH 


I 


.26 


.22 


.20 


.25 


.21 


.19 


.21 


.19 


H 


.29 


.25 


.23 


.28 


.25 


.22 


.24 


.22 


^=^=§1|l\> t 


G 


.32 


.28 


.25 


.30 


.27 


.25 


.26 


.24 


lS0mlmmS$ * 


F 


.34 


.30 


.27 


.33 


.30 


.27 


.29 


.27 


E 


.38 


.34 


.31 


.36 


.33 


.31 


.32 


.30 


X^p^^^^^ jo MF 


D 


.41 


.37 


.34 


.39 


.36 


.34 


.35 


.33 


G .75 


C 


.42 


.39 


.36 


.41 


.38 


.36 


.37 


.35 


Semidirect: Glass-Enclosed M -^ 


B 


.45 


.42 


.39 


.42 


.40 


.39 


.39 


.38 


three 40-Watt Lamps l &5 


A 


.47 


.44 


.41 


.45 


.42 


.40 


.41 


.39 


Spacing not 
to exceed 


J 


.27 


.25 


.19 


.26 


.22 


.19 


.20 


.18 


] x MH 


I 


.35 


.29 


.26 


.33 


.28 


.25 


.27 


.24 


H 


.3b 


.34 


.30 


.36 


.32 


.29 


.30 


.28 


25 


G 


.43 


.38 


.34 


.40 


.36 


.32 


.33 


.31 


-^2^3iC^> * 


F 


.46 


.41 


.37 


.43 


.39 


.35 


.37 


.33 




E 


.50 


.46 


.42 


.47 


.43 


.40 


.40 


.38 


<^0§§0^J 7 MF 


D 


.55 


.50 


.46 


.51 


.47 


.44 


.44 


.42 


'^ ~ <jo G .75 


C 


.58 


.53 


.49 


.53 


.49 


.46 


.46 


.44 


^^ M .65 


B 


.62 


.57 


.53 


.57 


.53 


.51 


.50 


.48 


Semidirect: Exposed Lamps P 5o 


A 


.64 


.60 


.56 


.59 


.55 


.52 


.51 


.49 


Spacing not 
to exceed 


J 


.24 


.19 


.16 


.22 


.18 


.15 


.16 


.14 


„1.2xMH 


I 


.29 


.25 


.22 


.27 


.23 


.20 


.21 


.19 


H 


.33 


.28 


.26 


.30 


.26 


.24 


.24 


.21 


I 1 


G 


.37 


.32 


.29 


.33 


.29 


.26 


.26 


.24 


F 


.40 


.36 


.31 


.36 


.32 


.29 


.29 


.26 


r^S » 


E 


.45 


.40 


.36 


.40 


.36 


.33 


.32 


.29 


vly 4* MF 


D 


.48 


.43 


.39 


.43 


.39 


.36 


.34 


.33 


G .75 


C 


.51 


.46 


.42 


.45 


.41 


.38 


.37 


.34 


General Diffuse : Totally M .70 


B 


.55 


.50 


.47 


.49 


.45 


.42 


.40 


.38 


Enclosed p - 65 


A 


.57 


-.53 


.49 


.51 


.47 


.44 


.41 


.40 


Spacing not 
to exceed 


J 


.26 


.21 


.18 


.22 


.19 


.16 


.16 


.15 




47 1.2 xMH 


I 


.31 


.26 


.24 


.27 


.24 


.22 


.21 


.19 




H 


.34 


.30 


.28 


.30 


.27 


.25 


.24 


.22 




t 


G 


.38 


.34 


.31 


.34 


.30 


.28 


.26 


.25 






F 


.41 


.37 


.33 


.36 


.33 


.30 


.28 


.27 


^ Jf^^ ' 


E 


.45 


.41 


.38 


.40 


.36 


.34 


.31 


.30 


v^ — °~"~ M MF 


D 


.49 


.45 


.42 


.42 


.41 


.37 


.34 


.33 


^^^. T ,. G .70 


C 


.51 


.48 


.44 


.44 


.44 


.39 


.36 


.34 


Direct-Indirect: jyj gg 


B 


.55 


.51 


.49 


.47 


.45 


.43 


.38 


.37 


Suspension Type p 59 


A 


.57 


.53 


.51 


.49 


.46 


.44 


.40 


.38 


Two 40-Watt Lamps 




















Spacing not 
to exceed 


J 


.24 


.20 


.17 


.23 


.19 


.16 


.18 


.16 




I 


.30 


.26 


.23 


.28 


.24 


.22 


.24 


.21 


1 . 2 x MH 


H 


.33 


.29 


.27 


.31 


.28 


.26 


.27 


.25 


^"T) ,8 


G 


.36 


.32 


.29 


.34 


.31 


.28 


.29 


.27 


^-^^/sS^y' ^ 


F 


.39 


.35 


.32 


.36 


.33 


.31 


.31 


.30 


^^J^ 00 ^ 7 MF 


E 


.42 


.39 


.36 


.40 


.37 


.35 


.35 


.33 


D 


.46 


.43 


.40 


.43 


.40 


.38 


.38 


.37 


" G .70 


C 


.48 


.45 


.42 


.44 


.42 


.40 


.40 


.38 


Semidirect: Ceiling Type p Vn 


B 
A 


.51 
.52 


.48 
.50 


.45 

.47 


.47 
.49 


.45 
.46 


.43 
.45 


.42 
.43 


.41 
.42 


Two 40-W 


att Lamps 























8-10 



I E S LIGHTING HANDBOOK 









Table 8-2 


. Continued 
















£ 


SPACING 


Ceiling. . . 


70% 


50% 


30% 
























LUMINAIRE 


hO 

85 

Q 


and Main- 
tenance 
Factor 


Walls 


50% 


30% 


10% 


50% 


30% 


io'/;, 


30% 


10% 




Room 
Index 




COEFFICIENT OF UTILIZATION 




Spacing not 
to exceed 


J 


.27 


.24 


.22 


.24 


.22 


.21 


.21 


.19 




1.2 xMH 


I 


.33 


.30 


.29 


.29 


.27 


.26 


.25 


.23 


^^^^ 46 


H 


.36 


.34 


.32 


.32 


.30 


.29 


.28 


.26 








G 


.39 


.37 


.35 


.36 


.33 


.32 


.30 


.28 






F 


.43 


.40 


.37 


.38 


.35 


.34 


.31 


.30 


r^ 




E 


.46 


.43 


.41 


.41 


.38 


.37 


.34 


.32 


.Tjrt^^^^^-^^^f*^ 3 ^ 33 


MF 


D 


.50 


.46 


.44 


.43 


.41 


.39 


.36 


.35 




G .65 


c 


.52 


.49 


.46 


.45 


.43 


.41 


.37 


.36 


Direct-Indirect: 
With Ribbed-Glass Bottom 


M .55 
P .50 


B 
A 


.55 

.56 


.52 
.54 


.50 
.52 


.47 
.49 


.45 

.47 


.44 
.45 


.38 
.40 


.37 
.38 


Four 40-Watt Lamps 


Spacing not 






















J 


.25 


.21 


.19 


.22 


.20 


.19 


.18 


.17 




to exceed 


I 


.30 


.28 


.27 


.27 


.25 


.24 


.22 


.21 


H^-r^^^lfc ' 


0.9 xMH 


H 


.33 


.31 


.30 


.29 


.27 


.26 


.25 


.24 




G 


.36 


.34 


.32 


.31 


.30 


.28 


.26 


.26 


s*g§^^^^ { 




F 


.38 


.36 


.34 


.33 


.31 


.30 


.28 


.27 




E 


.40 


.39 


.37 


.35 


.34 


.32 


.31 


.29 


45 


MF 


D 


.43 


.41 


.39 


.37 


.36 


.34 


.32 


.31 


Semidirect: With Ribbed- 


G .65 


C 


.45 


.43 


.40 


.39 


.37 


.36 


.33 


.32 


Glass Bottom, Ceiling Type 


M .55 


B 


.47 


.44 


.43 


.40 


.38 


.37 


.34 


.33 


Four 40-Watt Lamps 


P .50 

Spacing not 


A 


.48 


.46 


.44 


.41 


.39 


.38 


.35 


.34 




J 


.26 


.23 


.20 


.23 


.21 


.19 


.19 


.17 






to exceed 


I 


.31 


.28 


.27 


.28 


.26 


.24 


.23 


.20 






45 


1.2 xMH 


H 


.35 


.32 


.30 


.31 


.28 


.27 


.26 


.24 






t 




G 


.38 


.35 


.33 


.34 


.31 


.30 


.28 


.27 




^-^m^^ t 




F 


.41 


.38 


.35 


.36 


.34 


.32 


.30 


.28 


~~^ms ^^ * 




E 


.44 


.42 


.39 


.39 


.37 


.35 


.32 


.31 


^<%iZ02S9g&&^ 1 ^ 34 


MF 


D 


.48 


.45 


.42 


.42 


.39 


.38 


.34 


.33 




G .70 


C 


.50 


.49 


.44 


.43 


.41 


.39 


.35 


.34 


Direct-Indirect with Louvers 


M .65 


B 


.53 


.50 


.48 


.46 


.43 


.42 


.37 


.36 


Sus pension Type 


P .60 


A 


.54 


.52 


.50 


.47 


.45 


.43 


.39 


.37 


Four 40-Watt Lamps 


Spacing not 






















J 


.24 


.21 


.19 


.21 


.19 


.18 


.19 


.17 


-^sr-^~~> IS 


to exceed 


I 


.30 


.27 


.25 


.26 


.24 


.23 


.23 


.21 


^^^"^^Ssksk)! t 


0.9 xMH 


H 


.32 


.30 


.28 


.29 


.27 


.25 


.25 


.24 


-^^-^iiiiil^S^^*"/ — 




G 


.35 


.33 


.31 


.31 


.29 


.28 


.27 


.26 


x^^*0&i&^^^ \ 




F 


.35 


.35 


.32 


.32 


.31 


.29 


.29 


.27 


45 




E 


.4C 


.38 


.36 


.35 


.35 


.32 


.31 


.29 


Semidirect : "With Louvers, 


MF 


D 


.43 


.40 


.39 


.38 


.36 


.34 


.32 


.32 


Ceiling Type 


G .70 
M .65 


C 
B 


At 
.47 


.42 
.45 


.40 
.43 


.39 
.41 


.37 
.39 


.35 

.38 


.33 

.34 


.32 
.34 


Four 40-Watt Lamps 


P .60 

Spacing not 
to exceed 


A 


.48 


.46 


.44 


.42 


.40 


.38 


.35 


.34 




J 


.2C 


.16 


.13 


.16 


.13 


.11 


.10 


.09 


m ** 


I 


.24 


.20 


.18 


.20 


.17 


.15 


.13 


.12 


? ♦ 


1.2 x CH 


H 


.28 


.24 


.21 


.23 


.19 


.17 


.15 


.13 


- 




G 


.31 


.27 


.24 


.26 


.22 


.20 


.17 


.15 


^A \ 




F 


.34 


.30 


.27 


.28 


.24 


.22 


.19 


.17 


\ y 20 




E 


.38 


.34 


.31 


.31 


.27 


.25 


.21 


.19 


V___y ■<« 


MF 


D 


.45 


.38 


.35 


.34 


.30 


.28 


.23 


.22 


Semi-indirect: 


G .70 


C 


At 


.41 


.37 


.36 


.32 


.30 


.25 


.23 


Totallv Enclosed 


M .65 


B 


.4£ 


.45 


.42 


.39 


.36 


.34 


.27 


.25 










P .60 


A 


.51 


.47 


.44 


.41 


.38 


.36 


.28 


.27 



LIGHTING CALCULATIONS 



8-11 









Table 8-2. Continued 




















Ceiling. . 


70% 






50% 




30% 




_£ 


SPACING 






























LUMINAIRE 


11 

Q 


and Main- 
tenance 
Factor 


Walls. 


50% | 30% | 


10% 


50% 


30% 


10% 


30% | 10% 




Room 
Index 


COEFFICIENT OF UTILIZATION 


Spacing not 
to exceed 


J 


.18 


.14 


.12 


.14 


.11 


.09 


.08 


.07 


^- 70 1.2 x CH 


I 


.22 


.19 


.17 


.17 


.15 


.13 


.10 


.09 


H 


.26 


.22 


.19 


.20 


.17 


.15 


.12 


.10 


^T* 1 


G 


.29 


.25 


.22 


.22 


.19 


.17 


.14 


.12 


\zgSiTfr~ ~ 


F 


.32 


.28 


.25 


.24 


.21 


.19 


.15 


.14 


^^kss^iSSS^^ ^ 


E 


.35 


.32 


.29 


.27 


.24 


.21 


.17 


.15 


^^^SSS^ 000 ^ ii MF 


D 


.39 


.35 


.32 


.29 


.26 


.24 


.19 


.18 


G .60 


C 


.42 


.38 


.35 


.31 


.28 


.27 


.20 


.19 


Semi-indirect: M .50 


B 


.46 


.42 


.39 


.34 


.31 


.29 


.22 


.21 


Two 40-Watt Lamps P .40 


A 


.48 


.44 


.42 


.36 


.33 


.31 


.23 


.22 


Spacing not 
to exceed 
/^r\ 


J 


.16 


.13 


.11 


.12 


.10 


.08 


.06 


.05 


I 


.20 


.16 


.15 


.15 


.13 


.11 


.08 


.07 


< 


y 79 1.2xCH 


II 


.23 


.20 


.17 


.17 


.14 


.13 


.10 


.08 




t 


G 


.26 


.23 


.20 


.20 


.17 


.15 


.11 


.10 




1 


F 


.29 


.26 


.22 


.22 


.19 


.17 


.12 


.11 


, ' * ' MF 


E 
D 
C 


.32 

.36 


.29 
.32 
.35 


.26 
.30 
.32 


.24 
.26 

.28 


.21 

.24 


.19 
.22 


.13 
.15 
.16 


.12 
.14 
.15 


<*« 1 "II 1 1 m ' i\±JC 

^tp^ 3 G .65 


^38 


!25 


!24 


M .60 


B 


.42 


.39 


.36 


.30 


.29 


.27 


.18 


.17 


Indirect: Glass P .50 


A 


.44 


.41 


.39 


.33 


.30 


.29 


.19 


.18 


Spacing not 


J 


.17 


.14 


.12 


.13 


.11 


.09 


.07 


.06 




I 


.21 


.17 


.16 


.16 


.14 


.12 


.09 


.OS 


1.2 xCH 


H 


.24 


.21 


.18 


.18 


.15 


.14 


.11 


.09 


A 


G 


.27 


.24 


.21 


.21 


.18 


.16 


.12 


.11 


F 


.30 


.27 


.23 


.23 


.20 


.18 


.13 


.12 




* MF 


E 
D 


.33 
.37 


.30 
.33 


.27 
.31 


.25 

.27 


.22 
.25 


.20 

.23 


.14 
.16 


.13 


< ^"t> 


.15 


^^s^^ ° G .70 


C 


.39 


.36 


.33 


.29 


.26 


.25 


.17 


.16 


M .65 


B 


.43 


.40 


.37 


.31 


.30 


.28 


.19 


.18 


Indirect: Silvered Bowl P -55 


A 


.45 


.42 


.40 


.34 


.31 


.30 


.20 


.19 


Spacing not 
to exceed 


J 


.15 


.11 


.10 


.09 


.08 


.06 


.04 


.03 




I 


.19 


.15 


.13 


.12 


.10 


.09 


.06 


.04 


1.2 x CH 


II 


.22 


.19 


.16 


.14 


.12 


.10 


.07 


.05 




G 


.26 


.22 


.19 


.17 


.14 


.13 


.08 


.07 


^^iP so 


F 


.28 


.24 


.21 


.19 


.16 


.14 


.09 


.08 


^rlL^r~~~-. t 


E 


.32 


.28 


.25 


.21 


.18 


.17 


.11 


.10 


jl ^-"^afa^^? — MF 


D 


.35 


.31 


.29 


.23 


.21 


.19 


.12 


.11 


fZ^T\**^^^^^*~^ I G .60 


C 


.38 


.34 


.31 


.25 


.22 


.21 


.13 


.12 


^&^Z*~ M 5Q 


B 


.42 


.39 


.36 


.27 


.25 


.24 


.15 


.14 


P .40 


A 


.43 


.41 


.38 


.29 


.27 


.25 


.16 


.15 


Inc 


lirect 

























Room index may be obtained from Table 8-3 or these equations : 

indirect and semi-indirect luminaires; 

. , 2 X room width + length (feet) 

room mdex = - — — — . — ^~ 

4 X (ceiling height (feet) — 2.5) 

direct, semidirect, general diffuse, and direct- indirect luminaires; 

. , 2 X room width + length (feet) 

room mdex = -. — -. — ..,,„. ?r-=r 

6 X (mounting height (feet) — 2.5) 

It is current practice in tables (see 8-3) to use letter symbols. 



8-12 



I E S LIGHTING HANDBOOK 





Table 8-3. Room Indexes for a Wide Range of Room Sizes* 




0.6 


0.8 


1.0 


1.25 | 1.5 2.0 


2.5 3.0 1 4.0 1 5.0 






8y nbol 


J 


I 


H 


G F E 


D C B A 



CEILING HEIGHT (FEET) 



Semi-indirect and Indirect 
Luminaires 9 to 9^ 



10 to 12 to 14 to 17 to 21 to 25 to 
11* 13i 164 20 24 30 



31 to 37 to 
36 50 







MOUNTING HEIGHT ABOVE FLOOR (FEET) 










Direct, Semidirect, General 










1 












Diffuse, Direct-indirect Lu- 








10 to 


12 to 14 to 


17 to 


21 to 


25 to 


31 to 


37 to 






7 to n\ 


8 to 84. 


9 to 9| 


114 


13 4. | 16$ 


20 


24 


30 


36 


so 






ROOM 


ROOM 














WIDTH* 


LENGTH* 






room inde: 






(Feet) 


(Feet) 
















8-10 


H 


I 


J 


J 


















10-14 


H 


I 


I 


J 
















9 


14-20 


G 


H 


I 


J 


J 














(8h9) 


20-30 


G 


G 


H 


I 


J 


J 














30-42 


F 


G 


H 


I 


J 


J 


J 












42-up 


E 


F 


G 


H 


I 


J 


J 












10-14 


G 


H 


I 


J 


J 
















14-20 


G 


H 


I 


J 


J 


J 












10 


20-30 


F 


G 


H 


I 


J 


J 












(9|-10|) 


30-42 


F 


G 


G 


H 


I 


J 


J 












42-60 


E 


F 


G 


H 


I 


J 


J 












60-up 


E 


F 


F 


H 


H 


I 


J 












11-14 


G 


H 


I 


I 


J 


J 














14-20 


F 


G 


H 


I 


J 


J 












12 


20-30 


F 


G 


G 


H 


I 


J 


J 










(11-121) 


30-42 


E 


F 


G 


H 


I 


J 


J 












42-60 


E 


F 


F 


G 


H 


I 


J 












60-up 


E 


E 


F 


G 


H 


I 


J 












13-20 


F 


G 


H 


H 


I 


J 


J 












20-30 


E 


F 


G 


H 


I 


J 


J 


, 








14 


30-42 


E 


F 


F 


G 


H 


I 


J 


J 








(13-15J) 


42-60 


E 


E 


F 


F 


H 


I 


J 


J 


J 








60-90 


D 


E 


E 


F 


G 


H 


J 


J 


J 








90-up 


D 


E 


E 


F 


F 


G 


I 


J 


J 








16-20 


E 


F 


G 


H 


I 


J 


J 












20-30 


E 


F 


F 


G 


H 


I 


J 










17 


30-42 


D 


E 


F 


G 


H 


H 


J 


J 


J 






(16-181) 


42-60 


D 


E 


E 


F 


G 


G 


I 


J 


J 


J 






60-110 


D 


E 


E 


F 


G 


G 


1 


J 


J 


J 






110-up 


C 


D 


E 


E 


F 


G 


H 


I 


J 


J 






20-30 


D 


E 


F 


G 


H 


I 


J 


J 










30-42 


D 


E 


E 


F 


G 


H 


I 


J 


J 






20 


42-60 


D 


D 


E 


E 


F 


G 


I 


J 


J 


J 




(19-2U) 


60-90 


C 


D 


E 


E 


F 


G 


H 


J 


J 


J 






90-140 


c 


D 


D 


E 


F 


F 


H 


I 


1 


J 


J 




140-up 


c 


D 


D 


E 


F 


F 


H 


H 


1 


J 


J 



* For areas with dimensions greater than those shown in the table, use the following procedure to deter- 
mine the room index: 

1. Divide length and width by some common number which reduces dimensions to values within limits 
of table. 

2. Subtract 2| ft from the mounting height (or ceiling height) and divide this dimension by same divisor 
used in step 1. 

3. Add 2J ft to reduced height dimension and select the room index from the above table according to 
these new dimensions. 



LIGHTING CALCULATIONS 



8-13 



Table 8-3. Continued 



CEILING HEIGHT (FEET) 



Semi-indirect and Indirect 10 to 12 to 14 to 17 to 21 to 25 to 31 to 37 to 

Luminaires 9to9| 111 13| 16| 20 24 30 36 50 







MOUNTING HEIGHT ABOVE FLOOR (FEET) 










Direct, Semidirect, General 
























Diffuse, Direct- indirect 








10 to 


12 to 


14 to 


17 to 


21 to 


25 to 


31 to 


37 to 






7to7j 


8 to8i 


9 to9j 


HI 


13| 


16| 


20 


24 


30 


36 


50 


ROOM 


ROOM 






















WIDTH* 


LENGTH* 










ROOM INDE3 










(Feet) 


(Feet) 
























22-30 


D 


E 


E 


F 


G 


H 


I 


J 


J 








30-42 


C 


D 


E 


F 


G 


G 


I 


J 


J 






24 


42-60 


C 


D 


D 


E 


F 


G 


H 


1 


J 


J 




(22-26) 


60-90 


C 


D 


D 


E 


F 


F 


H 


I 


J 


J 


J 




90-140 


C 


C 


D 


E 


E 


F 


G 


H 


1 


J 


J 




140-up 


C 


c 


D 


E 


E 


F 


G 


H 


I 


I 


J 




27-42 


c 


D 


D 


E 


F 


G 


H 


I 


J 


J 






42-60 


c 


C 


D 


D 


F 


F 


H 


H 


I 


J 




30 


60-90 


B 


C 


C 


D 


E 


F 


G 


H 


I 


J 




(27-33) 


90-140 


B 


C 


C 


D 


E 


E 


F 


G 


H 


I 


J 




140-180 


B 


c 


c 


D 


E 


E 


F 


G 


H 


I 


J 




180-up 


B 


c 


c 


D 


E 


E 


F 


G 


H 


I 


J 




34-42 


B 


c 


D 


E 


F 


F 


H 


I 


I 


J 






42-60 


B 


c 


c 


D 


E 


F 


G 


H 


I 


J 


J 


36 


60-90 


A 


c 


c 


C 


E 


E 


F 


H 


H 


J 


J 


(34-39) 


90-140 


A 


B 


c 


C 


D 


E 


F 


G 


H 


I 


J 




140-200 


A 


B 


c 


C 


D 


E 


F 


F 


G 


H 


I 




200-up 


A 


B 


c 


C 


D 


E 


F 


F 


G 


H 


I 




40-60 


A 


B 


c 


c 


E 


F 


G 


H 


I 


I 


J 




60-90 


A 


B 


B 


c 


D 


E 


F 


G 


H 


I 


J 


42 


90-140 


A 


B 


B 


c 


D 


E 


E 


F 


G 


H 


J 


(40-45) 


140-200 


A 


A 


B 


c 


D 


D 


E 


F 


G 


H 


I 




200-up 


A 


A 


B 


c 


D 


D 


E 


F 


F 


G 


I 




46-60 


A 


A 


B 


c 


D 


E 


F 


G 


H 


I 


J 




60-90 


A 


A 


B 


c 


C 


D 


F 


F 


G 


H 


J 


50 


90-140 


A 


A 


A 


c 


C 


D 


E 


F 


F 


G 


I 


(46-55) 


140-200 


A 


A 


A 


c 


c 


D 


E 


E 


F 


G 


I 




200-up 


A 


A 


A 


c 


c 


D 


E 


E 


F 


G 


H 




56-90 


A 


A 


A 


B 


c 


D 


E 


F 


G 


H 


I 


60 


90-140 


A 


A 


A 


B 


c 


C 


D 


E 


F 


G 


H 


(56-67) 


140-200 


A 


A 


A 


B 


c 


C 


D 


E 


E 


F 


H 




200-up 


A 


A 


A 


B 


c 


C 


D 


E 


E 


F 


H 




68-90 


A 


A 


A 


A 


B 


C 


D 


E 


F 


G 


I 


75 


90-140 


A 


A 


A 


A 


B 


c 


D 


E 


F 


F 


H 


(68-90) 


140-200 


A 


A 


A 


A 


B 


B 


C 


D 


E 


F 


G 




200-up 


A 


A 


A 


A 


B 


B 


C 


D 


E 


F 


G 




90-140 


A 


A 


A 


A 


A 


B 


C 


D 


E 


F 


G 


90 or more 


140-200 


A 


A 


A 


A 


A 


B 


c 


D 


E 


F 


G 




200-up 


A 


A 


A 


A 


A 


B 


c 


c 


D 


E 


F 



8-14 I E S LIGHTING HANDBOOK 

The coefficient of utilization may be obtained from Table 8-2 or by compu- 
tation. In either case it is necessary to know, measure, or estimate the 
following: length, width, and ceiling height of the room; average luminous 
reflectance of walls and ceiling;* the candlepower distribution curve; and 
mounting height (above the floor) of the luminaire. 

The coefficient of utilization equals the total lumens utilized divided by 
the rated lamp lumens: 

F 

tu ~F t 

The total lumens emitted in each zone may be determined using the nomo- 
gram Appendix Fig. A-3 or the zonal constants in Appendix Table A-30 
and the distribution curve. The procedure for the zonal constants (sym- 
metric distribution) is as follows: 

1. Determine the lumens in each zone between degree and 180 degrees 
beginning at the intersection of the vertical axis and the bottom of the 
luminaire, by multiplying the average candlepower in each zone by the 
zonal constant. Tabulate these values, the rated lamp lumens, and H, 
the candlepower at 90 degrees, on a form such as Table 8-4. 

2. Obtain the following sums: 

Lumens in 0-degree to 40-degree zone (C) 
Lumens in 0-degree to 90-degree zone (D) 
Lumens in 90-degree to 180-degree zone (I) 

3. Determine per cent of flux in degree to 40 degree zone: 

r C - OMH 

/Y °- 40 ~ D - 5.0H 

Determine from Table 8-5 the classification of the direct component 
and enter in Table 8-4. Select from Table 8-5 the direct component mul- 
tiplying factor corresponding to the recorded ceiling and wall reflectances, 
room index, and component classification; enter in Table 8-4. 

4. Compute the directional components: 
Direct = (D) - 5 (//) 
Horizontal = 10 (H) 

Indirect = (7) - 5 (H) 
and enter the utilized lumens component, (F u ) — (directional component X 
multiplying factor), in Table 8-4. 

5. To obtain the coefficient of utilization for each room index, wall 
reflectance, and ceiling reflectance combination, add the three utilized 
lumen components and divide by the rated lamp lumens; enter in Table 8-4. 



* The average reflectance of a given wall area is determined by multiplying the area of each window, door, 
drapery, woodwork section, mirror, picture, tapestry, and so forth, by its reflectance and dividing the sum 
of the results by the total area. Since clear glass has a reflectance of only about 8 per cent, a full shade or 
Venetian blind with a reflectance of 50 to 80 per cent, when it is drawn to cover a window, will increase the 
average reflectance and, therefore, the utilization coefficient of a room. 



Table 8-4. Coefficient of Utilization Computation Sheet 



Room Index: 

Ceiling Reflectance (r c ): % 

Candlepower at 90° (H): 



Rated Lamp Lumens: (Fj) 

Wall Reflectance (r w ): % 



ZONE 
0°-10° 
10 -20 
20-30 
30^0 



40-50 
50-60 
60-70 
70-80 
80-90 



LUMENS 



ZONE 

90-100 
100-110 
110-120 
120-130 



LUMENS 



lumens 0°-40 o (C) 



130-140 
140-150 
150-160 
160-170 
170-180 



lumens 0°-90° (D) 



lumens 90M80 (/) 



Classification of direct component: 
Horizontal component = 10 (H) = 

Indirect component = (/) — 5 (H) = 
Direct component = (D) — 5 (H) = 









70% 












5n<£ 










inor. 








'" 






50% 


30% 


10% 


50% 


30% 


10% 


30% 










Room 
Index 


Com- 
ponent 


Mult. 
Factor 


"Fu 


Mult. 
Factor 


Fu 


Mult. 
Factor 


Fu 


Mult. 
Factor 


Fu 


Mult. 
Factor 


Fu 


Mult. 
Factor Fu 


Mult. 
Factor 


Fu 


Mult. 
Factor 


Fu 


J 


Ind 
Hor 
Dir 

Ku 


.19 
.21 

F u 

H =x ft 


.15 
.15 

1 


.13 
.11 




.13 
.19 

~~1 


.11 
.13 




.09 
.10 




.06 
.11 


.05 

.09 




0.6 


1 


| 


1 


i 
1 


I 


Ind 
Hor 
Dir 


.23 

.27 


.19 

.20 




.17 
.16 




.17 
.24 




.14 

.18 




.12 

.14 




.08 
.16 

"~1 


.07 
.13 




0.8 


K u 


| 


| 


i 




1 


1 


H 


Ind 
Hor 
Dir 


.27 
.31 

i 


.23 

.24 


.20 

.20 




.19 

.28 




.16 
.22 




.14 

.18 




.10 
.19 




.08 
.15 




1.0 


K u 


I 


| 


1 


1 


1 


■ i 
1 


G 


Ind 
Hor 
Dir 


.31 
.36 




.27 

.29 

1 

.30 

.33 

.34 

.39 

1 


.23 

.24 

1 


.23 
.31 

~~ 1 


.19 
.25 

~1 


.17 
.21 

~1 


.11 

.22 

~1 


.10 

.18 


1.25 


K u 


1 


"~ 1 


F 


Ind 
Hor 
Dir 


.34 

.40 




.26 
.27 

1 


.25 
.35 

1 

.28 

.40 

1 

.30 

.44 

~1 

.32 

.47 

1 


.21 
.29 




.19 
.24 




.12 
.25 




.11 
.21 


1.5 


K u 


1 


1 


1 


| 


| 


E 


Ind 
Hor 
Dir 


.38 

.46 

~1 


.31 
.35 

1 


.24 

.34 


.22 

.29 


.14 
.29 

~~ 1 


.13 

.25 


2.0 


K u 


1 




"1 


D 


Ind 
Hor 
Dir 

~ ~K~u 


.42 

.50 

~1 


.38 
.43 

1 


.35 

.37 




.27 
.38 

1 

.29 

.41 


.25 
.33 




.16 
.33 




.15 
.29 




2.5 


1 


| 


i 


1 


C 


Ind 
Hor 
Dir 


.45 
.54 




.41 
.47 




.38 
.41 


.27 
.36 




.17 
.36 

~1 


.16 
.32 


3.0 


K u 


I 


1 


■ i 
1 


1 


B 


Ind 
Hor 
Dir 

kZ 


.50 

.60 




.46 
.53 


.43 

.47 




.35 

.52 




.33 
.46 


.31 

.42 

~1 


.19 

.40 


.18 
.37 


4.0 


1 


| 


! 


1 


A 


Ind 
Hor 
Dir 


.52 

.63 




.48 
.57 




.46 
.51 




.38 
.55 


.35 
.49 




.33 

.45 




.21 

.42 




.19 
.40 


5.0 


K u 


1 


1 


1 


1 




1 


| 


1 


~~ 1 





' F u "■ directional component X multiplying factor. 



8-16 



I E S LIGHTING HANDBOOK 



Table 8-5. Universal Multiplying Factors for Direct Components of 
Utilization Coefficients 

DIRECT COMPONENT CLASSIFICATION 



Flux in 0° to 40" 
(Per cent) 


zone 




CLASSIFICATION 




35-40 




B 




. Broad 


40-45 




M 




. Medium 


45-50 




N 




. Narrow 


50-55 




VN 




. Very narrow 


55-60 




C 




. Concentrating 


More than 


60 


F 




Focusing 



Ceiling Re- 
flectance 


















0.75 






















0.5 






Direct Com- 


















ponent 
Classifica- 


B 


M 


N 


VN 


C 


F 


B 


M 


tion 


















Wall Re- 
flectance 


0.5 0.3 0.1 


0.5 


0.3 


0.1 


0.5 


0.3 


0.1 


0.5 


0.3 0.1 


0.5 


0.3 


0.1 


0.5 


0.3 


0.1 


0.5 


0.3 


0.1 


0.5 


0.3 


0.1 


Room Index 


MULTIPLYING FACTORS 


J-0.6 


.44 


.36 


.30 


.47 .4o!.35 


.5o'.44 


.40 


.53 .48 


.45 


.55 1. 51 


.45 


.57 


.54 


.52 


.431.36 


.30 


.46 


.40 


.35 


1-0.8 


.55 


.48 


.43 


.58 .521.48 


.481.61 


.56 


.64i.60 


.5(1 


.661.63 


.(12 


.68 


.66 


.65 


.541.47 


.42 


.57 


.51 


.47 


H-1.0 


.60 


.54 


.49 


.63 .58 .54 


.66. 62 


.59 


.69 .66 


.54 


.71 .69 


.68 


.73 


.72 


.71 


.59'. 54 


.49 


.62 


.58 


.54 


G-1.25 


.65 


.59 


.54 


.68 


.63 


.59 


.71 


.67 


.64 


.74 


.71 


.69 


.76'.74 


.73 


.78 


.77 


.76 


.64 .59 ! .54 


.67 


.63 .59 


F-1.5 


.69 


.63 


.58 


.72 


.67 


.63 


.75 


.71 


.67 


.7S 


.75 


.71 


.80 .78 


.75 


.82 .80 .78 


.671.62;. 58 


.70 


.66 .63 


E-2.0 


.75 


.7(1 


.65 


.78 


.74 


.70 


.80 


. i i 


.73 


.82 


.SO 


.77 


.84 .83 


.80 


.851. 841.83 


.74 .69,. 65 


.77 


.73 .70 


D-2.5 


.81 


.77 


.72 


.84 


.80 


.76 


.86 


.82 


.79 


.88 


.84 


.82 


.901.86 .84 


.91 .87'. 86 


.79;. 76J.72 


.82 


.79 .76 


C-3.0 


.84 


.80 


.76 


.86 


.83 


.79 


.88 


.85 


.81 


.90 


.871.83 


.91 


.891.85 


.92 ! .90 


.87 


-82 1 .78 ! .76 


.84 


.81 .79 


B-4.0 


.88 


.85 


.82 


.90 


.87 


.84 


.91 


.88 


.86 


.92 


.89 .88 


.93 


.901.89 


.93 .91 


.90 


.861. S3!. 81 


.88 


.851.83 


A-5.0 


.91 


.87 


.84 


.92 


.89 


.86 


.93 


.90 


.87 


.94 


.91 .89 


.94 


.92 .90 


.94 .93 

- 


.91 


.89 .85 .83 


.90 


.871.85 



Ceiling Re- 












0.5 






















0.3 


















Direct Com- 






















ponent 
Classifica- 


N 


VN 


C 


F 


B 


M 


N 


VN 


C 


F 


tion 






















Wall Re- 


0.5 


0.3 


0.1 


0.5 0.3 0.1 


0.5 


0.3 0.1 


0.5 0.3 


0.1 


0, 


0.1 


0.3 


0.1 


0.3 


0.1 


0.3 


0.1 


0.3 


0.1 


0.3 


0.1 






Room Index 


MULTIPLYING FACTORS 


J-0 . fi 


.4<)|.44 


.40 


.521.48 .45 


.541.51 


.49 


.561.54 .52 


.35 


.30 


.39 


.35 


.43 


.40 


.48 


.44 


.52 


.48 


.56 


.51 


1-0.8 


.60 .55 


.52 


.63'. 591.57 


.65 


.62 


.61 


.67 


.65 .64 


.47 


.42 


.51 


.47 


.55 


.52 


.59 


.56 


.02 


.59 


.65 


.62 


H-1.0 


.65 


;62 


.5!! 


.68 


.65'.63 


.70 


.68 


.67 


.72 


.71 


.70 


.53 


.49 


.57 


.54 


.61 


.69 


.65 


.63 


.68 


.66 


.71 


.69 


G-1.25 


.70 


.67 


. 64 


.73 


.70 


.68 


.75 


.73 


.71 


.77 


.75 


.74 


.57 


.54 


.61 


.59 


.65 


.64 


.69 


.68 


.72 


.71 


.75 


.73 


F-l 5 


.73 


.70 


.67 


.75 


.73 


.71 


.77 


.76 


.74 


.79 


.78 


.77 


.61 


.58 


.65 


.63 


.69 


.67 


.73 


.71 


.76 


.74 


.78 


.76 


E-2.0 


.79 


.76 


.73 


.81 


.79 


.76 


.83 


.81 


.79 


.84 


.83 


.81 


.68 


.65 


.72 


.70 


.75 


.73 


.78 


.76 


.80 


.78 


.82 


.80 


D-2.5 


.84 


.81 


.79 


.86 


.83 


.81 


.87 


.85 .83 


.88 


.86 


.85 


.75 


.72 


.78 


.76 


.80 


.79 


.82 


.81 


.84 


.83 


.85 


.84 


C-3.0 


.86 


.83 


.81 


.88 


.85 


.83 


.89 


.87 


. 85 


.90 


.88 


.86 


.77 


.75 


.80 


.78 


.82 


.80 


.84 


.82 


.85 


.84 


.86 


.85 


B-4.0 


.89 


.86 


.85 


.90 


.87 


.86 


.91 


.88 


.87 


.91 


.89 


.88 


'.82 


.80 


.84 


.82 


.85 


.84 


.86 


.85 


.87 


.86 


.88 


.87 


A-5.0 


.91 


.88 


.86 


.92 


.89 


.87 


.92 


.90 


.88 


.92 


.90 


.89 


.84 


.82 


.86 


.,4 


.87 


.85 


.88 


.86 


.89 


.87 


.89 


.88 



LIGHTING CALCULATIONS 8-17 

AVERAGE BRIGHTNESS 

It has long been realized that brightness as well as illumination must be 
considered in lighting design. Recently a committee of the Illuminating 
Engineering Society developed a simple method of predicting average 
brightness values in interiors. 6 The procedure, based on the original work 
of Buckley, 7 Hisano, 8 Yamauti, 9 Moon, 10 and Spencer, 10 is as follows: 

1. Obtain the average maintained illumination level (E av ), using Ta- 
ble 8-1 or the lumen method and record on a form such as Table 8-6 with 
the data indicated. 

2. Compute and enter in Table 8-6 the room coefficient k r (similar in 
concept to the room index) using the following equation: 

, Ml + w) 

k r = ■ » 

2 Iw 

where h — ceiling height I = length of room w = width of room 

3. The average maintained brightnesses (in footlamberts) of various 
areas may now be determined using the equations of Table 8-6. 

The best conditions for critical seeing are those for which the ratio of any 
of the brightness values just given to the brightness of the task falls 
within the range §-3. 6 



Table 8-6. Average Brightness Calculation Sheet 6 

Average maintained illumination E av = footcandles 

Typ3 of lighting: Direct □; General Diffuse Q; Indirect Q. 
Average reflectance : 

task (rt) floor (77) 

working plane (r p ) wall (r w ) (seenote.) 

ceiling (r e ) 

Room dimensions: ceiling height (h) ft; length (I) ft; width (w) ft 

Room coefficient: k r = — ^— ; = 

2 Iw 

Brightnesses 

Task: B t = E av X r t = footlamberts 

Working plane: B v = E av X r p = footlamberts 

Floor: B s = E av X -J~ = footlamberts 

Ej av 
T> J. 

Walls midway to ceiling: B mw = E av X " = footlamberts 

D + 

Walls near ceiling: B tw = E av X -Jr- = footlamberts 

Ceiling: B e = E av X ~ = footlamberts 

* From Table 8-7A. t From Table 8-7C. 
f From Table 8-7B. § From Table 8-7D. 

Note: The average reflectance of a given wall area is determined by multiplying the area of each window, 
door, drapery, woodwork section, mirror, picture, tapestry, and so forth, by its reflectance and dividing the 
sum of the results by the total area. Since clear glass has a reflectance of only about 8 per cent, a full shade 
or Venetian blind with reflectance of 50 io 80 per cent, when it is drawn to cover a window, will increase 
the average reflectance and, therefore, the utilization coefficient of a room. 



8-18 



I E S LIGHTING HANDBOOK 



Table 8-7. Brightness Ratios For Direct, Indirect, and General Diffuse 
Lighting Installations in a Variety of Rooms 6 

A. AVERAGE FLOOR BRIGHTNESS (£,)/AVERAGE 
ILLUMINATION LEVEL (E av ) 



Ceiling reflectance 




















0.8 




0.7 




0.5 








Wall reflectance 






















0.5 


0.3 


0.1 


0.5 


0.3 


0.1 


0.5 


0.3 


1 






Room coefficient 














Kr 














Direct and 














Indirect 






floor reflectance 


?7 = 0.3 






Lighting 














0.1 


0.290 


0.288 


0.286 


0.290 


0.288 


0.286 


0.290 


0.288 


0.286 


0.2 


.280 


.277 


.273 


.280 


.277 


.273 


.280 


.277 


.273 


0.3 


.271 


.266 


.261 


.271 


.266 


.261 


.271 


.266 


.261 


0.4 


.262 


.255 


.249 


.262 


.255 


.249 


.262 


.255 


.249 


0.5 


.253 


.245 


.237 


.253 


.245 


.237 


.253 


.245 


.237 


0.7 


.236 


.226 


.216 


.236 


.226 


.216 


.236 


.226 


.215 


1.0 


.213 


.200 


.188 


.213 


.200 


.188 


.213 


.200 


.186 


Direct and 














Indirect 






floor reflectance 


r, = 0.1 






Lighting 














0.1 


0.096 


0.096 


0.095 


0.096 


0.096 


0.095 


0.096 


0.096 


0.095 


0.2 


.093 


.092 


.091 


.093 


.092 


.091 


.093 


.092 


.091 


0.3 


.090 


.088 


.087 


.090 


.088 


.087 


.090 


.088 


.087 


0.4 


.087 


.085 


.083 


.087 


.085 


.083 


.087 


.085 


.083 


0.5 


.083 


.081 


.079 


.083 


.081 


.079 


.083 


.081 


.079 


0.7 


.078 


.075 


.072 


.078 


.075 


.072 


.078 


.075 


.072 


1.0 


.070 


.066 


.062 


.070 


.066 


.062 


.070 


.066 


.062 


General 














Diffuse 






floor reflectance 


r f = 0.3 






Lighting 














0.1 


0.298 


0.295 


0.293 


0.298 


0.296 


0.294 


0.300 


0.297 
.293 


0.295 


0.2 


.295 


.291 


.287 


.296 


.292 


.288 


.299 


.291 


0.3 


.292 


.287 


.282 


.293 


.289 


.284 


.298 


.289 


.287 


0.4 


.289 


.283 


.277 


.291 


.285 


.280 


.296 


.285 


.284 


0.5 


.286 


.280 


.274 


.288 


.282 


.276 


.295 


.281 


.281 


0.7 


.281 


.275 


.268 


.2S4 


.278 


.271 


.295 


.274 


.277 


1.0 


.275 


.270 


.263 


.279 


.274 


.266 


.288 


.265 


.274 


General 














Diffuse 






floor reflectance 


77 = 0.1 






Lighting 














0.1 


0.099 


0.099 


0.098 


0.100 


0.099 


0.098 


0.010 


0.099 


0.099 


0.2 


.098 


.097 


.092 


.099 


.098 


.096 


.100 


.099 


.097 


0.3 


.097 


.096 


.091 


.098 


.096 


.095 


.099 


.098 


.096 


0.4 


.096 


.095 


.091 


.097 


.095 


.093 


.099 


.097 


.095 


0.5 


.095 


.093 


.090 


.096 


.094 


.092 


.098 


.096 


.094 


0.7 


.093 


.091 


.088 


.094 


.092 


.090 


.097 


.095 


.093 


1.0 


.091 


.089 


.087 


.092 


.091 


.089 


.095 


.093 


.091 



LIGHTING CALCULATIONS 



8-19 



Table 8-7. Continued 

AVERAGE WALL BRIGHTNESS HALFWAY BETWEEN FLOOR AND 
CEILING (£„,,„) /AVERAGE ILLUMINATION LEVEL {E av ) 



Ceiling reflectance 






















0.8 




0.7 






0.5 








Wall reflectance 






















0.5 


0.3 


0.1 


0.5 


0.3 


0.1 


0.5 


0.3 


0.1 






Room coefficient 
















Kr 
















Direct and 
















Indirect 






floor reflectance 


?7 = 0.3 






Lighting 
















0.1 


0.332 


0.198- 


0.657 


0.332 


0.198 


0.657 


0.332 


0.198 


0.656 


0.2 


.340 


.202 


.667 


.340 


.202 


.667 


.340 


.202 


.667 


0.3 


.348 


.206 


.680 


.348 


.206 


.680 


.348 


.206 


.680 


0.4 


.357 


.212 


.697 


.357 


.212 


.697 


.357 


.212 


.696 


0.5 


.367 


.218 


.717 


.367 


.218 


.717 


.367 


.218 


.716 


0.7 


.389 


.231 


.765 


.388 


.231 


.765 


.388 


.231 


.762 


1.0 


.426 


.256 


.856 


.426 


.256 


.856 


.426 


.256 


.851 


Direct and 
















Indirect 






floor reflectance 


r f = 0.1 






Lighting 
















0.1 


0.288 


0.172 


0.057 


0.288 


0.172 


0.057 


0.288 


0.172 


0.057 


0.2 


.300 


.179 


.059 


.300 


.179 


.059 


.300 


.179 


.059 


0.3 


.313 


.186 


.082 


.313 


.186 


.062 


.313 


.186 


.062 


0.4 


;327 


• 194. 


.064 


.327 


.194 


.064 


.327 


.194 


.064 


0.5 


.340 


.202 


.067 


.340 


.202 


.067 


.340 


.202 


.067 


0.7 


.368 


.220 


.073 


.368 


.220 


.073 


.368 


.220 


.073 


1.0 


.413 


.249 


.083 


.413 


.249 


.083 


.413 


.249 


.083 


General 
















Diffuse 






floor reflectance 


r, = 0.: 


} 






Lighting 
















0.1 


0.442 


0.268 


0.090 


0.453 


0.274 


0.092 


0.478 


0.289 


0.098 


0.2 


.455 


.278 


.095 


.464 


.284 


.097 


.490 


.298 


.010 


0.3 , 


.466 


.287 


.099 


.476 


.294 


.010 


.500 


.306 


.011 


0.4 l 


.478 


.297 


.010 


.488 


.304 


.105 


.512 


.313 


.111 


0.5 


.490 


.307 


.107 


.450 


.314 


.110 


.523 


.320 


.115 


0.7 


.514 


.328 


.117 


.523 


.334 


.119 


.545 


.334 


.125 


1.0 


.551 


.359 


.131 


.559 


.364 


.133 


.576 


.354 


.138 


General 
















Diffuse 






floor reflectance 


r/ = 0.] 


. 






Lighting 
















0.1 


0.415 


0.252 


0.085 


0.424 


0.257 


0.087 


0.447 


0.271 


0.091 


0.2 


.427 


.262 


.085 


.437 


.268 


.091 


.460 


.382 


.096 


0.3 


.441 


.272 


.091 


.450 


.278 


.096 


.473 


.293 


.010 


0.4 


.454 


.283 


.096 


.464 


.289 


.010 


.487 


.304 


.106 


0.5 


.46S 


.294 


.010 


.477 


.300 


.105 


.500 


.315 


.110 


0.7 


.496 


.316 


.112 


.505 


.322 


.115 


.525 


.336 


.120 


1.0 


.538 


.350 


.127 


.545 


.356 


.130 


.562 


.368 


.135 



8-20 



I E S LIGHTING HANDBOOK 



Table 8-7. Continued 

C. AVERAGE WALL BRIGHTNESS NEAR CEILING (fi M( )/AVERAGE 
ILLUMINATION LEVEL (#«„) 



Ceiling reflectance 






















0.8 




0.7 






0.5 








Wall reflectance 






















0.5 


0.3 


0.1 


0.5 


0.3 


0.1 


0.5 


0.3 


0.1 






Room coefficient 
















Kr 
















Direct and 
















Indirect 






floor reflectance 


r f = 0.3 






Lighting 
















0.1 


0.351 


0.210 


0.070 


0.351 


0.210 


0.070 


0.351 


0.210 


0.070 


0.2 


.382 


.229 


.077 


.382 


.229 


.077 


.382 


.229 


.077 


0.3 


.418 


.253 


.085 


.418 


.253 


.085 


.418 


.253 


.085 


0.4 


.459 


.281 


.096 


.459 


.281 


.096 


.459 


.281 


.096 


0.5 


.506 


.314 


.011 


.506 


.314 


.011 


.506 


.314 


.011 


0.7 


.618 


.397 


.141 


.618 


.397 


.141 


.618 


.397 


.141 


1.0 


.084 


.057 


.214 


.084 


.057 


.214 


.084 


.057 


.212 


Direct and 
















Indirect 






floor reflectance 


r/ = 0.1 






Lighting 
















0.1 


0.311 


0.187 


0.062 


0.311 


0.186 


0.062 


0.311 


0.186 


0.062 


0.2 


.351 


.211 


.070 


.351 


.211 


.070 


.351 


.211 


.070 


0.3 


.394 


.239 


.080 


.394 


.239 


.OSO 


.394 


.239 


.080 


0.4 


.441 


.270 


.092 


.441 


.270 


.092 


.441 


.270 


.092 


0.5 


.493 


.306 


.011 


.493 


.306 


.011 


.493 


.306 


.011 


0.7 


.614 


.393 


.140 


.614 


.393 


.140 


.614 


.393 


.140 


1.0 


.085 


.057 


.213 


.085 


.057 


.213 


.085 


.057 


.213 


General 












_ 




Diffuse 






floor reflectance 


77 = 0. 


3 






Lighting 
















0.1 


0.450 


0.273 


0.092 


0.459 


0.279 


094 


0.482 


0.292 


0.099 


0.2 


.472 


.289 


.099 


.479 


.294 


.100 


.498 


.304 


.010 


0.3 


.492 


.306 


.011 


.499 


.310 


. 107 


.514 


.316 


.111 


0.4 


.516 


.324 


.113 


.520 


.327 


.115 


.532 


.329 


.117 


0.5 


.540 


.344 


.122 


.543 


.345 


.123 


.549 


.342 


.125 


0.7 


.591 


.386 


.140 


.589 


.385 


.140 


.584 


.368 


.140 


1.0 


.671 


.455 


.172 


.661 


.449 


.170 


.636 


.409 


.166 


General 
















Diffuse 






floor reflectance 


r f = 0.1 


L 






Lighting 
















0.1 


0.425 


0.258 


0.087 


0.434 


0.263 


0.089 


0.454 


0.275 


0.093 


0.2 


.449 


.276 


.090 


.457 


.280 


.096 


.474 


.291 


.099 


0.3 


.474 


.295 


.099 


.480 


.299 


.010 


.495 


.308 


.011 


0.4 


.501 


.315 


.011 


.505 


.318 


.111 


.516 


.325 


.114 


0.5 


.528 


.336 


.117 


.530 


.338 


.120 


.537 


.342 


.122 


0.7 


.584 


.381 


.137 


.582 


.380 


.138 


.577 


.378 


.138 


1.0 


.671 


.453 


.170 


.660 


.447 


.169 


.636 


.433 


.165 



LIGHTING CALCULATIONS 



8-21 



Table 8-7. Continued 

D. AVERAGE CEILING BRIGHTNESS (£ C )/AVERAGE ILLUMINATION 

LEVEL (E av ) 



Ceiling reflectance 


0.8 


0.7 




0.5 








Wall reflectance 


0.5 


0.3 


0.1 


0.5 


0.3 


0.1 


0.5 


0.3 


1 






Room coefficient 
Kr 





















Direct 
Lighting 



0.1 
0.2 
0.3 
0.4 
0.5 
0.7 
1.0 



Direct 
Lighting 



0.1 
0.2 
0.3 
0.4 
0.5 
0.7 
1.0 



Indirect 
Lighting 



0.1 
0.2 
0.3 
0.4 
0.5 
0.7 
1.0 



0.1 
0.2 
0.3 
0.4 
0.5 
0.7 
1.0 



floor reflectance 77 = 0.3 



0.261 


0.238 


0.216 


0.223 


0.204 


0.185 


0.149 


0.136 


0.123 


.266 


.221 


.180 


.226 


.190 


.154 


.151 


.127 


.010 


.271 


.212 


.153 


.232 


.181 


.131 


.154 


.121 


.087 


.283 


.208 


.134 


.243 


.178 


.115 


.162 


.118 


.076 


.299 


.210 


.120 


.257 


.180 


.010 


.171 


.120 


.069 


.345 


.229 


.108 


.296 


.196 


.092 


.197 


.131 


.062 


.045 


.204 


.118 


.038 


.252 


.010 


.257 


.168 


.068 



floor reflectance rj = 0.1 



0.115 


0.096 


0.077 


0.098 


0.082 


0.066 


0.066 


0.055 


.142 


.011 


.071 


.012 


.091 


.061 


.081 


.061 


.171 


.119 


.067 


.046 


.010 


.057 


.097 


.068 


.200 


.133 


.066 


.071 


.114 


.056 


.011 


.076 


.231 


.149 


.067 


.098 


.128 


.057 


.132 


.085 


.299 


.190 


.074 


.256 


.162 


.064 


.171 


.011 


.425 


.274 


.102 


.365 


.235 


.087 


.243 


.157 



floor reflectance 77 = 0.3 



floor reflectance 77 = 0.1 



0.044 
.040 
.038 
.037 
.038 
.043 
.058 



1.108 


1.129 


1.151 


1.108 


1.129 


1.151 


1.108 


1.129 


1.228 


1.277 


1.326 


1.228 


1.277 


1.326 


1.228 


1.277 


1.363 


1.446 


1.528 


1.363 


1.448 


1.528 


1.363 


1.448 


1.514 


1.638 


1.761 


1.514 


1.638 


1.761 


1.514 


1.638 


1.682 


1.856 


2.030 


1.682 


1.856 


2.030 


1.682 


1.856 


2.078 


2.386 


2.699 


2.078 


2.386 


2.699 


2.078 


2.386 


2.861 


3.481 


4.138 


2.861 


3.481 


4.318 


2.861 


3.481 



1.151 
1.326 
1.529 
1.759 
2.027 
2.691 
4.112 



1.114 


1.134 


1.153 


1.114 


1.134 


1.152 


1.114 


1.134 


1.241 


1.285 


1.328 


1.241 


1.285 


1.328 


1.241 


1.285 


1.381 


1.457 


1.531 


1.381 


1.457 


1.531 


1.381 


1.457 


1.537 


1.651 


1.765 


1.537 


1.651 


1.765 


1.537 


1.651 


1.710 


1.872 


2.035 


1.710 


1.872 


2.035 


1.710 


1.872 


2.113 


2.406 


2.705 


2.113 


2.406 


2.705 


2.113 


2.406 


2.906 


3.506 


4.146 


2.906 


3.506 


4.146 


2.905 


3.506 



1.152 
1.328 
1.531 
1.765 
2.035 
2.705 
4.146 



8-22 



I E S LIGHTING HANDBOOK 









Table 8-7. D 


Continued 








Ceiling reflectance 




















0.8 




0.7 




0.5 








Wall reflectance 






















0.5 


0.3 


0.1 


0.5 


0.3 


0.1 


0.5 


0.3 








Room coefficient 
Kr 




General 














Diffuse 






floor reflectance r/ = 0., 


3 






Lighting 














0.1 


0.634 


0.633 


0.631 


0.589 


0.587 


0.586 


0.479 


0.477 


0.476 


0.2 


.694 


.693 


.650 


.642 


.643 


.645 


.522 


.520 


.524 


0.3 


.748 


.758 


.767 


.694 


.702 


.762 


.561 


.563 


.577 


0.4 


.805 


.826 


.848 


.745 


.764 


.849 


.602 


.606 


.635 


0.5 


.864 


.898 


.936 


.797 


.830 


.942 


.640 


.650 


.697 


0.7 


.982 


1.054 


1.135 


.902 


.969 


1.144 


.715 


.740 


.833 


1.0 


1.167 


1.310 


1.483 


1.062 


1.195 


1.485 


.825 


.878 


1.061 


General 














Diffuse 






floor reflectance r/ = 0.J 








Lighting 














0.1 


0.564 


0.563 


0.561 


0.523 


0.522 


0.521 


0.425 


0.424 


0.423 


0.2 


.634 


.637 


.612 


.589 


.591 


.593 


.478 


.480 


.481 


0.3 


.703 


.712 


.699 


.651 


.660 


.669 


.527 


.535 


.543 


0.4 


.769 


.789 


.792 


.711 


.731 


.751 


.574 


.590 


.607 


0.5 


.835 


.869 


.891 


.771 


.803 


.838 


.619 


.645 


.675 


0.7 


.967 


1.036 


1.104 


.888 


.953 


1.026 


.704 


.757 


.819 


1.0 


1.166 


1.305 


1.465 


1.061 


1.190 


1.345 


.824 


.929 


1.055 



Luminaire Spacing 

In planning general-lighting systems the aim is to provide a uniform 
level of illumination throughout the room. To make the entire area 
equally suitable for whatever its use may be, spottiness and dark corners 
are eliminated so far as possible. The maximum permissible spacing be- 
tween luminaires and from luminaires to side-walls for equal uniformity 
is a function of the mounting height above the floor and the distribution 
characteristics of the luminaires. Figure 8-la and b dramatizes the effect 
of variations in spacing. 

In general, with greater mounting height and closer spacing greater uni- 
formity is achieved. The variation factor which equals the maximum 
illumination level divided by the average level is used as a measure of uni- 
formity. A spacing which does not substantially exceed the mounting 
height above the floor usually will result in reasonably uniform illumination. 

Table 8-2 gives the maximum spacing of common types of luminaires 
with which reasonably uniform illumination may be obtained. The dis- 
tance between luminaire and side-wall should not exceed one-half the dis- 
tance between luminaires. For equal uniformity where aisles or storage 
spaces are adjacent to walls and where desks and benches are along walls 
the distance between luminaires and walls should not exceed one-third to 
one-quarter the spacing between luminaires. 

The spacing-mounting height relations apply not only to individual lumi- 



LIGHTING CALCULATIONS 



8-23 




FIG. 8-1. Proper spacing of luminaires, as in a, results in uniform illumination. 
When luminaires are spaced too far apart, as in b, the resulting illumination is non- 
uniform. 

naires but to the spacing between continuous sections, luminous panels, 
troughs, or sections of coves. 

Spacing of alternate mercury and incandescent units in combination 
systems should provide for a fair degree of uniformity with either system 
used alone, as well as for overlapping and blending of the light when used 
in combination. An alternate staggered layout with the spacing between 
units not to exceed eight-tenths of the mounting height above the floor 
often is satisfactory. 

To retain symmetry with the arrangement of bays, columns, partitions, 
or other architectural elements closer spacing than indicated in Table 8-2 
is desirable. Closer spacing will improve uniformity and reduce shadows 
at any given point. A few typical lavouts of luminaires are given in 
Fig. 8-2. 11 



p j'o a 
i> io ojo o Jo o 

P o\0; o.(.C' *o; o. a 
<) o >o. of fi o xo-: o 



FOUR UNITS PER BAY 



". i. . ' • . I '. • (', 

• of v je- a-!- c Jo. 

:OJ o' to tf p 

■;6,iS<> ;}p;:;oi; : c no 



FOUR-TWO SYSTEM 




ONE UNIT PER BAY 




FIG. 8-2. Typical luminaire layouts in various interiors. See Section 10 for discussion. 



8-24 



I E S LIGHTING HANDBOOK 



Floodlighting Calculations 

Typical floodlighting installations and equipment are shown in Fig. 8-3. 




PROJECTOR DISTANCE 
FROM SURFACE 



BUILDINGS TWO OR THREE 
STORIES HIGH LIGHTED FROM 
POSTS AT CURB 



FLOODLIGHTS MAY BE PLACED ON CURBPOSTS OR WIDE 
MARQUEES TO LIGHT SMALL STORES, TH EATRES, ETC., WHEN 
SUITABLE POSITIONS ACROSS THE STREET ARE NOT AVAILABLE. 



WHEN LENGTH OF BUILDING FACE TO BE ILLUMINATED IS NOT 
GREATER THAN DISTANCE OF FLOODLIGHTS FROM BUILDING, THE 
UNITS CAN BE PLACED IN ONE GROUP. 




LIGHTED SURFACE 



LESS THAN 3,000 SQ FT 



MORE THAN 3000 SQ FT 



LESS THAN 3,000 SQ FT 



MORE THAN 3,000 SQ FT 



LESS THAN 10,000 SQ FT 



MORE THAN iO.OOO SQ FT 



ONE-STORY 



TWO-STORY 



THREE-STORY 



FOUR-STORY OR MORE 



UNITS ARE PLACED IMMEDIATELY INSIDE AND BELOW PARAPET 
AND ELEVATED SUFFICIENTLY TO PERMIT EASY MAINTENANCE 
AND AVOID DRIFTING SNOW. 



BEST PROJECTOR LOCATIONS ARE MOST SATISFACTORILY DE- 
TERMINED BY TRIAL. STATUES USUALLY REQUIRE LIGHT FROM 
ABOVE TO AVOID GROTESQUE EFFECT UPON HUMAN FEATURES 
CAUSED BY LIGHT FROM BELOW. 



AT EDGE OF AREA 



UNITS SHOULD BE MOUNTED NOT LESS THAN 20 FEET HIGH 
AND LOCATED WHERE THEY WILL NOT HINDER TRAFFIC OR 
CAUSE ACCIDENTS DUE TO GLARE 




AT EDGE OF AREA 



TO INSURE THAT GLARING LIGHT SOURCES WILL NOT BE IN 
THE DIRECT LINE OF VISION, IT IS ADVISABLE TO MOUNT 
PROJECTORS AS HIGH AS POSSIBLE. 



LAMP 



GS 



GS 



GS 

F 



GS 



GS 



GS 



* PROJECTOR BEAM SPREAD I W = WIDE, M = MEDIUM , N-NARROW 
** DEPENDING ON LENGTH OF THROW 
GS = GENERAL SERVICE F=FLOODLIGHTING 

FIG. 8-3. Typical floodlighting applications and equipment, 
discussion. 



See Section 11 for 



LIGHTING CALCULATIONS 



8-25 



Coverage. Area of spot is the principal concern in checking for coverage. 
Length and width of spot are also given. These are found useful in prob- 
lems involving the lighting of architectural details and also when it is desired 
to illuminate a limited area. 

After projector location is determined, guidance for collecting the data 
essential to a coverage check is given in Fig. 8-4. 

The number of projectors required for reasonably uniform coverage is 
obtained by dividing the total area to be lighted by the spot area of one 
projector. 

Floodlighting installations also can be laid out to scale with a protractor, 
a method which provides an aiming diagram as well as coverage check, and 
also by other methods. 19 



AVERAGE AREA 
LIGHTED 




FIG. 8-4. Spot sizes (average effective coverage) for typical beam spreads and 
installation arrangements are given in Table 8-8. D = the distance from the pro- 
jector to the plane of the lighted surface or area, measured perpendicular to the sur- 
face. Z = the measurement which determines the average angle of throw and con- 
sequently determines the average area covered by each projector. Two conditions 
apply: (1) If a perpendicular from the plane of the lighted surface to the projector 
falls within the total area to be lighted, Z = one half the distance from the base of the 
perpendicular to the farthest edge of the surface to be lighted. (2) If a perpendicu- 
lar from the plane of the lighted surface to the projector falls outside the total area 
to be lighted, Z = the distance from the base of the perpendicular to the mid-point 
of the total area to be lighted. 

Illumination. To determine the number of luminaires required to pro- 
duce any desired average level of illumination over a known area, or the 
necessary beam lumens where the number of projectors is known, use the 
following formula: 12 



Number of projectors = 



tL av X A 



k m X Fb 
where 

E av = maintained average illumina- 
tion level (footcandles) 
A = area of surface to be lighted 
(square feet) 



= maintenance factor (usually 

assumed to be 0.70) 
= initial lumens in the beam 



8-26 



I E S LIGHTING HANDBOOK 



Table 8-8. Dimensions and Areas of Illuminated Spots Produced by 
Various Types and Arrangements of Floodlights.* 12 (See Fig. 8-4.) 





zt 


10° BEAM 


15° BEAM 


20° BEAM 


25° BEAM 


Df 


< 


to 

c 

3 

4 

7 

14 

22 


J3 

•3 

js 

3 
3 
4 

6 

8 


ctf 
o 

< 

10 

20 

50 

130 

290 


■5 

to 
c 

>J 

4 

6 

11 

21 

37 


is 


< 


to 
c 
a; 


-6 
% 

5 

7 
9 
13 
17 


CI) 

< 


J3 

cm 

c 

►3 

7 
10 
20 
41 

83 




15 



10 
20 
30 
40 


5 

8 

21 

52 

113 


4 
5 

7 
9 
12 


18 

33 

93 

250 

620 


5 

8 

16 
30 
55 


30 

50 

160 

460 

1.300 


7 
8 
12 
17 
23 


25 



20 
40 
60 
80 


11 

23 

71 

195 

450 


4 

16 
31 
54 


4 
5 

8 
11 
15 


25 

50 

170 

490 

1.200 


7 
11 
25 
49 
90 


7 

8 

13 

18 

24 


44 

100 

330 

1,630 

2,920 


9 
15 
34 
73 
145 


9 
12 
17 
25 
36 


70 

150 

540 

1.960 

7.270 


11 

19 

45 

105 

251 


11 

14 
22 
34 
53 


50 




20 
40 
60 
80 


38 
47 
81 
150 
260 


9 
11 
14 
22 
32 


9 
9 
11 

14 
17 


90 

no 

190 
340 
600 


13 

15 
22 
33 
49 


13 

14 
17 
20 
25 


155 
195 
330 
630 
1,160 


18 
21 
30 

45 
68 


18 
1-9 
23 
28 
35 


210 

320 

550 

1,076 

2,060 


20 
26 
38 
58 
90 


20 
24 
29 
36 
45 


75 



40 
80 
120 
160 


67 

110 

220 

530 

1,040 


13 

17 
28 
48 
76 


13 
14 
18 
25 
32 


170 

250 

546 

1,210 

2,500 


20 
25 

43 
74 
119 


20 
22 
29 
38 
49 


310 

440 

1.010 

2,320 

5,050 


26 
34 
59 
102 

171 


26 
30 
39 
52 
67 


480 

710 

1,636 

3,936 

9,060 


33 
43 
75 
135 

238 


33 
38 
50 

67 
88 


100 




40 

80 

120 

160 

200 


120 
150 
250 
470 
830 
1,300 


17 
20 
29 
43 
63 
SO 


17 
19 
22 
28 
33 
42 


310 
390 
580 
890 
1,950 


26 
31 
44 

66 
98 


26 

28 
34 
41 
51 


490 
616 
1,650 
2,000 
3,700 
6,650 


35 
41 
59 
90 
136 
201 


35 

38 
46 
56 
69 
84 


770 

980 

1,700 

3,290 

6,340 


44 
52 
75 

116 
180 


44 
48 
58 
72 
89 


150 



40 
80 
120 
160 
200 


270 
300 
400 
570 
860 
1,280 


26 

28 
34 
43 
57 

74 


26 
27 
30 
34 
39 
44 


610 

680 

900 

1,310 

1,970 


39 
42 
51 

65 
86 


39 
41 
45 
51 
58 


1.100 
1,230 
1,630 
2,380 
3,610 
5,550 


S3 
57 

69 
89 
117 
156 


53 
55 

60 
68 
79 
91 


1,740 
1.940 
2,580 
3.820 
5,920 


67 
71 
87 
113 
151 


67 
69 
76 
87 
100 


200 



40 

80 
120 
160 
200 


480 
510 
600 
770 
1,030 
1,370 


35 

37 
41 
48 
58 
71 


35 
38 

38 
41 
45 
50 


1,090 
1,160 
1,360 
1,730 
2,330 


53 
55 
61 

72 
87 


53 

54 
57 
61 

68 


1,940 
2,080 
2,470 
3,166 
4,246 
5,860 


71 
73 
82 
97 
118 
146 


71 

72 
77 
83 
91 
102 


3,096 
3,288 
3.916 
5,636 
6,860 


89 
92 
104 
123 
150 


89 
91 
96 
104 
115 


300 



40 
80 
120 
160 


1,080 
1,110 
1,200 
1,350 
1 ,580 


52 
53 
56 
61 

6S 


52 
53 
54 
57 
60 


2,460 
2,520 
2,720 
3,070 
3,590 


79 

so 

So 

92 
102 


79 

SO 
S2 
85 
90 


4,400 
4,520 
4,890 
5,530 
6,480 


106 
108 
114 
123 
137 


106 
107 
110 
114 
120 


6,940 
7,140 
7,740 
8,796 
10,300 


133 
136 
143 
156 
173 


133 
134 
138 
144 

152 


500 



40 
80 
120 
160 


3,010 
3,030 
3,120 
3,270 
3,490 


87 
88 
90 
93 
97 


87 
S8 
89 
90 
92 


6,810 
6,870 
7,070 
7,410 
7,900 


132 
133 
135 
139 
145 


132 
132 
133 
135 
138 


12,200 
12 ,300 
12,700 
13,300 
14 .200 


176 

177 
181 
187 
195 


176 
177 
179 
1S1 
185 


19,300 
19 ,500 
20,100 
21,100 
22,500 


222 
223 
228 
235 
246 


222 
222 
225 
228 
233 



The beam lumens rating of a particular luminaire is often provided by the manu- 
facturer or may be computed from a candlepower distribution curve as follows: 

1. On a form such as Table S-9 record the following data: 

Maximum intensity, I max (candlepower) 
Angle at 10 per cent I max (degrees) 

2. Compute beam spread: 

Spread = 2X (angle at 10 per cent I maz ) (degrees) ; 



LIGHTING CALCULATIONS 



8-27 













Table 8-8. 


Continued 














Z 


30' 


BEAM 


35 


BEAM 


D 


z 


4C 


"BEAM 


50 


° BEAM 


D 




_G 


« 




A 


J3 




■S 


& 




fj 








































aj 


a 




0> 




.'H 








a 




u 


a 


x> 






< 


J 


8 


< 


h-1 


9 






< 


►J 


P» 


< 


>J 


[S 







45 


8 


60 


9 







80 


11 


11 


130 


14 


14 




10 


80 


12 


10 


110 


14 


12 




5 


110 


13 


12 


175 


17 


16 


15 


20 


240 


26 


14 


360 


32 


17 


15 


10 


150 


17 


14 


260 


22 


18 




30 


790 


56 


21 


1,430 


79 


27 




15 


310 


25 


19 


530 


33 


25 




40 


2,900 


133 


33 


8.690 


622 


50 




20 


630 


43 


23 


1,250 


63 


30 




















25 


1.150 


65 


27 




— 


— 







100 


13 


13 


140 


16 


16 







185 


18 


18 


305 


23 


23 




10 


140 


16 


15 


170 


19 


17 




10 


240 


22 


2() 


400 


28 


26 




20 


220 


23 


IS 


310 


28 


20 




20 


450 


33 


24 


800 


44 


32 


25 


30 


430 


36 


21 


660 


45 


27 


25 


30 


970 


55 


32 


2,050 


83 


44 




40 


920 


59 


28 


1,430 


75 


34 




40 


2.300 


98 


42 


6,950 


187 


66 




50 


1,930 


94 


37 


3.270 


131 


45 




50 


6,450 


194 


60 


— 


— 


— 




60 


3,950 


155 


46 


8,590 


249 


63 























350 


27 


27 


510 


32 


32 







320 


26 


26 


520 


33 


33 




20 


450 


33 


29 


650 


37 


34 




10 


380 


28 


27 


580 


37 


32 


50 


40 


800 


46 


35 


1,160 


55 


41 


35 


20 


510 


35 


32 


890 


47 


39 




60 


1,590 


73 


44 


2,440 


90 


53 




30 


850 


49 


35 


1,550 


67 


47 




80 


3,200 


117 


56 


5 ,300 


151 


69 




40 


1,490 


71 


43 


3,000 


105 


59 




















50 


2,700 


106 


52 


— 


— 


— 







700 


40 


40 


970 


47 


47 







470 


33 


33 


780 


43 


42 




20 


790 


43 


42 


1,070 


51 


49 




10 


520 


35 


34 


820 


44 


42 




40 


1,060 


53 


46 


1,460 


63 


54 




20 


650 


40 


37 


1.070 


52 


" 4? 


75 


60 


1,590 


69 


53 


2,200 


83 


61 


45 


30 


890 


49 


42 


1,550 


67 


53 




80 


2,480 


93 


61 


3,620 


114 


73 




40 


1,320 


66 


46 


2,460 


91 


62 




100 


4,000 


128 


72 


5,780 


160 


84 




50 


2.100 


87 


55 


— . 


-_- 


— . 




120 


6,400 


175 


84 


10.100 


226 


103 























1.130 


64 


54 


1.560 


63 


63 







640 


40 


40 


1,030 


51 


51 




4C 


1,430 


63 


58 


1,980 


74 


68 




20 


790 


46 


44 


1,300 


59 


56 


100 


80 


2,550 


92 


70 


3,560 


110 


82 


55 


40 


1,320 


66 


51 


2,330 


88 


68 




120 


5,050 


146 


89 


7,510 


180 


106 




60 


2,650 


104 


65 


5,250 


152 


8S 




160 


10 .300 


234 


112 


— 


— 


— 




80 


5,600 


172 


83 


— 


— 


— 







1,760 


67 


67 


2.440 


79 


79 







1.020 


51 


51 


1,680 


65 


63 




40 


2,130 


73 


71 


2.870 


88 


83 




20 


1,180 


55 


54 


1,940 


73 


69 


125 


80 


3,090 


97 


80 


4,350 


116 


96 


70 


40 


1,680 


71 


60 


2,860 


83 


7S 




120 


5.200 


138 


96 


7,430 


167 


113 




60 


2,700 


98 


70 


5.00Q 


135 


94 




160 


9,140 


200 


116 


— 


— 


— 




80 


4,700 


142 


84 


— 


— 


— 







2.540 


80 


80 


3,510 


95 


95 







1,500 


62 


62 


2,460 


79 


79 




40 


2,880 


86 


85 


3,900 


102 


97 




20 


1,680 


67 


64 


2,750 


85 


82 


150 


80 


3,820 


105 


92 


5,300 


125 


108 


85 


40 


2.130 


78 


69 


3,600 


102 


90 




120 


5.700 


135 


107 


8,000 


166 


123 




60 


3.080 


100 


78 


5,400 


133 


103 




160 


10,300 


234 


112 










80 
100 


4,750 
7,500 


132 

181 


92 
106 


— 


— 


— 







4,500 


107 


107 


6.250 


126 


126 







2,100 


73 


73 


3.400 


93 


93 




40 


4.800 


111 


109 


6,660 


132 


129 




20 


2,280 


78 


74 


3.700 


98 


m 


200 


80 


5,700 


125 


116 


7,950 


149 


136 


100 


40 12.700 


86 


79 


4.500 


112 


103 




120 


7,500 


150 


127 


10 ,3C0 


178 


148 




60 13.500 


104 


87 


7,800 


138 


113 




160 


10,200 


184 


141 


— 


— 


-- 




80 5,000 


13Q 


98 


-ee 


-= 


— . 




— ' 












- 




100 |7,300 


168 


110 


— 


— 


— 



* Allowance made for necessary beam overlap. 

f Dimensions may be in feet and square feet or in other units if more convenient 



3. Record (on Table 8-9) constants from Appendix Table A-31 page A-47, for 
not less than ten zones equal in width to about one tenth the beam spread. Measure 
or estimate and record on Table 8-9 the average candlepower for each zone. 

4. Compute zonal lumens F z : 

F z = Iz av X zonal constant. 
The sum of the zonal lumens in each zone from degree to the angle at 10 per cent 
I max equals the beam lumens. 



8-28 I E S LIGHTING HANDBOOK 

Table 8-9. Form for Use in Calculating Beam Lumens in Floodlights, 
Spotlights,* and Searchlights.* 

Maximum intensity candlepower 

Angle at 10-per-cent maximum intensity degrees 

Beam spread = 2 X (angle at 10-per-cent 7 max ) = degrees 



ZONES* 



1. 
2. 
3. 
4. 
5. 
6. 
7. 
8. 
9. 
10. 



/ IN 70NFt ZONAL F z (ZONAL 

lav UN ^uiMiiT CONSTANT^ LUMENS) 



X 
X 
X 
X 
X 
X 
X 
X 
X 
X 



Note. Lumens in the beam (Fb) equal the sum of the zonal lumens in the zones between degree and angle 
at 0.1 /max- Fb = 2S" 1 JmaxF, = 

* If the beam is very narrow (as in searchlights) this computation is made by summing up the lumens in 
a group of rectangular solid angles enclosed by the beam . Average candlepower measurements at the center 
of rectangular areas subtending not less than one tenth the beam spread in horizontal and vertical directions 
are used. The total number of solid angles used is 100, for which the constants are found in Appendix Ta- 
ble 000. 

t From distribution curve or measurements. 

t Zone width should not exceed one tenth the beam spread for best results. 

§ From Appendix Table 31, page A-47. 

Searchlighting Calculations 

Lumens in searchlight beams may be estimated in the manner just de- 
scribed for floodlights. 

The illumination on a circular area in a searchlight beam may be deter- 
mined by dividing the area by the lumens in the zones subtended by the 
area, and multiplying by the atmospheric transmittance. 

The useful range of searchlights can be calculated with the aid of the 
following formulas: 



,2 It 



E a — Eb ?> or E a — Eb 



rK 

R 2 



where E a — necessary illumination at observer's position for 

viewing object 
Eb = actual illumination at 1 mile 
t = atmospheric transmittance (0.6 per mile for aver- 
age clear weather) 
d\ = max distance, searchlight to visible object 
0I2 — max distance object visible to observer 
K = reflectance of object 
R = useful range of searchlight beam 



LIGHTING CALCULATIONS 



8-29 



Show-Window Lighting 

For estimating average illumin- 
ation in show windows, two planes 
are frequently used to represent the 
average display surfaces as shown in 
Fig. 8-5. These vary in size and po- 
sition in different windows. They 
are divided into zones A, B, and C 
to permit designing for either a var- 
iation in illumination level between 
parts of the display or for a uniform 
level equally effective throughout. 

Footcandles produced at differ- 
ent distances by projector and re- 
flector lamps are given in Fig. 8-6. n 

In selecting a zone for use in 
estimating average illumination, 
consider the nature of the trim and 
whether the back will be open or 
closed (see Store Lighting, Section 
10) and proceed as follows : 

1. Record the dimensions H, D, 
nation, E av . 

2. Compute the following ratios 

650 



600 
550 




FIG. 8-5. Show windows are divided 
into three zones (A, B, and C) when it is 
desired to estimate the number of lamps 
necessary for a given illumination level. 



L, and the desired average illumi- 



Height (to bottom of luminaire) 



in 500 

LU 

_i 

§450 

< 

k400 
O 

o 

"- 350 



z 300 

O 

£250 

z 

I 200 



150 AND 300 -WATT . 
R-40 REFLECTOR ( 


.. ZONE 


LUMENS 
150 300 










1 0-5 ° 150 340 








"I 0-10 


- 4/u a/s 




















PROJECTION 
DISTANCE 




1 f 


PROJECTION 








I DIST 

Y 


ANCE IN FEET: 


COVER 


^geT 




VI 










1/ / 
II i 


\ \l 










1 l 


\ 1 

\ \ 
1 \ 




.AMPS 
0-WATT 
0-WATT 






J-' 5 
I i 

/I ' r 


1 \ 

5«1 


15 






w 














Jgl\ 








^^fj?* 


*~~~\£ 


~*^C 


S?§s= 





Depth 



H 
D 



Length _ L 
Height ~ H 




2 4 664 2 

DISTANCE FROM CENTER OF BEAM IN FEET 



FIG. 8-6. Illumination produced at various distances by typical reflector and pro- 
jector lamps. 



8-30 



I E S LIGHTING HANDBOOK 



3. From Table 8-10 obtain multiplying (K), length (L), and shielding (S) 
factors. 

4. The initial lumens to be provided per linear foot of window: 

F f = E av HKLS 
where E av = average illumination maintained in 

service (assuming maintenance fac- 
tor - 0.75) 
H = height in feet 
K = multiplying factor 
L = length factor 
S = shielding factor 

Necessary initial lumens per incandescent lamp 

F/ X lamp spacing (inches) 
12 



Necessary feet of fluorescent lamps 



Ft 



initial lumens per foot of lamps 



X window length 



Table 8-10. Constants for Use in Calculating Average Maintained 
Illumination in Typical Show Windows* 20 

A. MULTIPLYING FACTOR K FOR INCANDESCENT LUMINAIRESf 



H/D 
Ratio 


ZONE A 


ZONE B 


ZONE C 


OVER-ALL 


Wide 


Semi- 
cone. 


Cone. 


Wide 


Semi- 
cone. 


Cone. 

3.9 

4.1 
4.5 
5.0 
5.5 
6.3 
7.5 


Wide 


Semi- 
cone. 


Cone. 


Wide 


Semi- 
cone. 


Cone. 


4.0 

3.5 
3.0 
2.5 
2.0 

1.5 
1.0 


4.2 
3.6 
3.2 
3.0 
2.9 
3.0 
3.3 


3.4 
3.0 
2.6 
2.4 
2.3 
2.4 
2.9 


2.0 
1.8 
1.7 
1.7 
1.7 
1.9 
2.3 


6.8 
6.0 
5.5 
4.6 
4.3 
4.1 
4.6 


5.5 
5.0 
4.6 
4.0 
3.7 
3.6 
4.1 


1.6 

1.8 
2.0 
2.4 
3.1 
4.1 
7.5 


2.0 
2.3 
2.8 
3.7 
5.1 
8.3 
20.3 


3.0 
3.6 
4.1 
5.0 
6.1 
9.4 
20.0 


2.8 
2.9 
3.0 
3.1 
3.3 
3.6 
4.4 


3.4 
3.1 
3.2 
3.3 
3.4 
3.6 
4.3 


2.9 
3.0 
3.1 
3.2 
3.4 
3.6 
4.3 



B. MULTIPLYING FACTOR K FOR FLUORESCENT LUMINAIRESf 



H/D 

Ratio 


ZONE A 


ZONE B 


ZONE C 


OVER-ALL 


Wide 


Semi- 
cone. 


Cone. 


Wide 


Semi- 
cone. 


Cone. 


Wide 


Semi- 
cone. 


Cone. 


Wide 


Semi- 
conc. 


Cone. 


4.0 
3.5 
3.0 
2.5 
2.0 
1.5 
1.0 


4.9 
4.6 
4.2 
4.1 
4.1 
4.0 
4.3 


5.7 
5.2 
4.2 
3.9 
3.8 
3.6 
3.6 


4.2 
3.9 
3.4 
3.0 

2.7 
2.4 
2.3 


11.3 
9.2 
7.9 
6.2 
5.7 
5.2 
5.0 


10.3 
9.2 
6.9 
5.0 
4.3 
4.4 
5.0 


7.6 
6.8 
5.6 
4.7 
3.7 
4.1 
6.8 


2.7 
2.3 
2.5 
2.8 
3.3 
4.3 
7.6 


1.5 

1.6 

1.8 
2.2 
2.8 
4.1 
7.6 


1.7 

1.9 

2.2 
2.7 
3.7 
5.7 
15.1 


3.8 
3.8 
4.0 
4.0 
4.1 
4.5 
5.3 


3.0 
3.1 
3.1 
3.3 
3.5 
4.0 
4.7 


2.7 
2.S 
2.9 
3.1 
3.3 
3.6 
4.2 



LIGHTING CALCULATIONS 



8-31 



Table 8-10. Continued 

C. LENGTH FACTOR L FOR INCANDESCENT LUMINAIRES 





LENGTH OF WINDOW DIVIDED BY HEIGHT (L/H) 


TYPE OF EQUIPMENT 


0.5 


1.0 


1.5 


2.0 


§ 


1 Glass 
end 


Solid 
ends 


1 Glass 
end 


Solid 
ei_ds 


1 Glass 
end 


Solid 
ends 


1 Glass 
end 


Solid 
ends 


Wide 

Semi-Cone. 

Cone. 


1.40 
1.30 
1.20 


1.25 
1.20 
1.10 


1.10 
1.05 
1.00 


1.05 
1.00 
1.00 


1.00 
1.00 
1.00 


1.00 
1.00 
1.00 


1.00 
1.00 
1.00 


0.95 
0.95 
1.00 



D. LENGTH FACTORS L FOR FLUORESCENT LUMINAIRES 



LENGTH OF WINDOW DIVIDED BY HEIGHT (L/H) 



0.5 


1.0 


1.5 


2.0 


1 Glass end Solid ends 


1 Glass end 


Solid ends 


1 Glass end 


Solid ends 


1 Glass end 


Solid ends 


1.55 


1.45 


1.20 


1.10 


1.00 


0.95 


0.95 


0.90 



E. SHIELDING FACTOR S FOR INCANDESCENT LUMINAIRES|| 



H/D 
Ratio 



4.0 

3.5 
3.0 
2.5 

2.0 

1.5 
1.0 



LOUVERS AT RIGHT AN- 


LOUVERS PARALLEL TO 


GLES TO PLATE GLASS 


PLATE GLASS 


' Zone A 


Zone B 


Zone C 
1.4 


Zone A 


ZoneB 


Zone C 


1.3 


1.4 


1.2 


1.4 


2.2 


1.3 


1.4 


1.4 


1 


2 


1 


4 


2.3 


1.3 


1.4 


1.5 


1 


2 


1 


5 


2.6 


1.3 


1.4 


1.6 


1 


2 


1 


6 


3.0 


1.4 


1.4 


1.6 


1 


2 


1 


8 


3.7 


1.4 


1.5 


1.7 


1 


2 


1 


9 


4.6 


1.4 


1.5 


1.8 


1 


3 


2 


1 


5.3 



ECCENTRIC RING LOUVERS 



Zone A 



Zone B Zone C 



Not usually employed 
Not usually employed 
Not usually employed 
Not usually employed 



1.4 
1.4 
1.4 



1.6 
1.8 
2.2 



2.9 
3.3 
4.0 



F. SHIELDING FACTOR S FOR FLUORESCENT LUMINAIRES| 







SHIELDING FACTOR S 




H/D RATIO 


Egg-crate Louvers (Mat White) Shielding Lamps to 45° Crosswise and 25° 
Lengthwise 




Zone A 


Zone B 


Zone C 


4.0 




1.20 


1.14 


3.5 




1.20 


1.14 


3.0 




1.18 


1.14 


2.5 




1.18 


1.14 


2.0 




1.18 


1.16 


1.5 


1.09 


1.15 


1.19 


1.0 


1.09 


1.10 


1.27 



* Maintenance factor used = 0.75. 

t Table based on typical commercial equipment. 

t This table is based on the coefficients of utilization for four rows of fluorescent lamps in reflectors of 
typical widths, at typical angles of tilt. If other numbers of rows and different widths of unit or other angles 
of tilt are employed, some differences in results are to be expected. These may be greatest when the rearmost 
of the multiple rows approach zone C. 

§ Output: wide 65 per cent; semiconcentrating S5 per cent; concentrating SO per cent. 

II Faotor for unshielded lamps = 1.00. 



8-32 



I E S LIGHTING HANDBOOK 



Showcase Lighting 

Typical arbitrary trim lines used for showcase lighting calculations are 
the same as those shown in Fig. 8-5 for show windows. Plane A extends 
from the lower front edge of the case to a point one-third of the case height 
above the base. Plane C-B runs from the top back corner to a point that is 
one-half case depth. Zones B and C are equal in area. One, two, or per- 
haps all three zones will be important depending on the method of display- 
ing the merchandise. 

To estimate the average initial illumination on a zone in one of the cases, 
substitute the proper value for the utilization factor K u in the following 
formula: 

Footcandles on zone = K „ X F f 20 



where 



F f = lumens per foot of case length 
K u — utilization factor from Ta- 
ble 8-11. 



The value of F f for either filament or fluorescent lamps will be: 

Ft XN 



F f = 



L 



where 



Ft — initial lumen output of each lamp 
N = number of lamps 
L = length of case (feet) 



Table 8-11. Utilization Factors, K u , for Typical 20-Inch Showcase, 
10, 20, or 27 Inches High. 20 


ZONE 


FLUORESCENT 
LAMP IN WHITE 
DIFFUSING RE- 
FLECTOR 


FLUORESCENT 
LAMP IN CON- 
CENTRATING 
REFLECTOR 


INCANDESCENT 
LAMP, CLEAR 
T-10 IN SEMI- 
DIFFUSING RE- 
FLECTOR 


INCANDESCENT 

LAMP T-10 

REFLECTOR 

SHOWCASE 


HEIGHT 

(inches) 


A 
B 

c 


0.266 
.122 
.051 


0.321 
.198 
.093 


0.219 

.137 
.095 


0.356 
.359 
.128 


10 


A 
B 
C 


.170 
.137 
.081 


.165 
.192 
.139 


.143 
.119 
.122 


.226 
.333 
.184 


20 


A 
B 
C 


.129 
.112 
.094 


.123 
.145 
.150 


.108 
.093 
.121 


.179 
.238 
.207 


27 



LIGHTING CALCULATIONS 



8-33 



Shelf and Garment Case Lighting 

To aid in estimating the average initial illumination normal to the 
vertical surface representing the plane of the merchandise in shelves or 
garment cases lighted by a continuous row of fluorescent lamps, the surface 
may be divided into 6-inch sections as shown in Fig. 8-7. 

The initial footcandles normal to any 6-inch section can be computed by 
substituting values in the following equation: 

Footcandles = K u F f 
where K u = utilization factor (Fig. 8-7) 

Ff = lumens-per-foot rating of the lamps used. 20 

Two values of K u for the centerpoint of each 6-inch section are given in 
Fig. 8-7 for merchandise plane depths of 3 inches, 6 inches, 9 inches, 12 
inches, and 18 inches. The upper of each pair of figures is the factor for a 
continuous row of fluorescent lamps shielded by a cornice painted white 
underneath. The lower figures are for the same lamps, fitted with a con- 
centrating reflector aimed at the bottom of the vertical plane assumed to 
be 4 feet high. Where the height is less than 4 feet, the reflector would be 
aimed higher and some increase in the footcandle values would result. 



3 IN. 

-»j \— |«6IN.*j 



f«--9INr-»" 




ICO' 

0.600 
0.342 

0.185 
0.121 

0.027 
0.061 

0.0 1 1 
0.028 

0.006 
0.0/6 

0.004 
0.0/0 

0.003 
0.008 



0.002 0.005 

0.006 [0.0/3 

VERTICAL FOOTCANDLES = K 



aco 



0.402 
0.1 56 



0.159 
0.125 



0.060 
0.095 



0.028 
0.056 



0.018 
0.034 



0.010 
0.028 



0.007 
0.017 



[•—-1 2 IN.--.-*] 

,■,:.■ ' ! -11111111111 



V 18 IN. 



4iO 



0.269 
0.041 



0.175 
0.135 



0.084 
0.097 



0.044 
0.077 



0.026 
0.051 



0.017 
0.036 



0.011 
_ 0.026 



HtO 



0.206 
0.03/ 



0.165 
0.096 



0.098 

C.094 



0.057 
0.086 



0.035 
0.062 



0.023 
0.044 



0.016 
_ 0.033 



VALUES OF K, 



0.008 0.012 0.018 

0.020 1 0.031 1 0.037 

(SHOWN ABOVE) X LUMENS-PER-FOOT OF LIGHT SOURCE 



0.135 
0.028 



0.129 
0.080 



0.098 
0.084 



0.068 
0.090 



0.047 
0.077 



0.032 
0.059 



0.023 
0.048 



UPPER FIGURES FOR FLUORESCENT LAMP, NO REFLECTOR, CORNICE WHITE 

FINISH. 

LOWER FIGURES FOR FLUORESCENT LAMP, CONCENTRATING REFLECTOR AIMED 

AT BOTTOM OF TIER OF SHELVES. 



FIG. 8-7. Multiplying factors K u used in computing the illumination (normal to a 
vertical surface representing the merchandise on shelves or in garment cases) pro- 
duced by a continuous row of fluorescent lamps. Lower figures are for installations 
including a concentrating reflector; upper figures for installations without reflector. 



8-34 



I E S LIGHTING HANDBOOK 



Luminous Elements 

The efficiencies of a number of typical luminous elements are given in 
Table 8-12. The maintained average brightness of a specific element 
may be obtained from the following formula: 



B e 



EFiNK, 
A 



where B av — maintained average brightness of ele- 

ment (footlamberts) 
E = efficiency of element (from Table 8-12) 

(per cent) 
F( = initial lumen output per lamp 
N = number of lamps 
K m — maintenance factor 
A — luminous area (square feet) 

Values computed with this formula, assuming a maintenance factor of 
0.70, are given in Table 8-13. 



Table 8-12. Efficiencies of Various Forms of Luminous Elements 1 



TYPE OF ELEMENT 



DIMENSIONAL 
RATIOS 




0.33 W 
0.50 W 
1.5 D 

(W - C) s 





pSs_ 




\ 




- 







D = 0.25 W 

S = 0.56 W 

S = 2.25 D 

A = WS 



REFLECTANCE OR TRANSMIT- 
TANCE 



0.20 0.30 0.40 



0.60 0.70 



0.80 



Element Efficiency (%) 



12 16 | 20 j 24 j 28 32 



Width based on 5 to 1 varia- 
tion of brightness from cen- 
ter to edge. Concavity of 
surface produces greater 
uniformity of brightness; 
convexity increases shading. 
In design of cross-section, 
trough cutoff and angle of 
view are very important. 



10 13 



17 20 23 



27 



Requires polished metal 
parabolic trough reflectors 
with maximum candlepower 
directed to the far edge of 
surface. With ratios given 
brightness graduations will 
be of the order of 25 to 1 ; the 
degree of shading can be 
lessened by the use of a 
larger, more concentrating 
reflector, and by increasing 
D with respect to W. 



LIGHTING CALCULATIONS 



8-35 



Table 8-12. Continued 



TYPE OF ELEMENT 




. ' < >ffiffi^v'^? 




p ' 






"/If: 





> 


/« 
/I 







DIMENSIONAL 
RATIOS 



D = 0.33 W 
S = 0.33 W 
S = D 

A = (W - C) S 



(For 2 rows of 

lamps) 
D = 0.33 W 
S = 0.50 W 
S = 1.5 D 
A = 0.50 WS 



D = 0.40 W 

S = 0.60 W 

S = 1.5D 

A = WS 



D = 0.33 W 
S = 0.66 W 
S = 2D 

A = (W - C) S 



REFLECTANCE OR 
TRANSMITTANCE 



0.20 1 0.30 


0.40 1 0.50 


0.60 


0.70 


0.80 


Element Efficiency (%) 


7 


10 


13 


17 


20 


23 


27 



Slightly graduated bright- 
ness produced by lamps at 
one side; uniformity if lamps 
are located on each side 
with a ratio as given. In 
small elements make cer- 
tain that dimensions allow 
for easy lamp replacement. 



25 



35 


44 


51 


56 


61 



65 



Representative of a great 
variety of forms ranging 
from a narrow band requir- 
ing a single row of lamps to 
large expanses of luminous 
glass areas requiring a wide 
variety of lamp arrange- 
ments. Efficiencies vary 
slightly with size and form, 
but spacing between lamps 
should conform to the cavity 
depth and type of translu- 
cent material used. 



26 37 46 54 60 66 70 



Lamps should be placed in 
the corner to permit wider 
spacing and better lateral 
uniformity of brightness 
with highly diffusing ma- 
terials. A slight shading of 
brightness at the sides may 
be noticed. In small ele- 
ments tubular or Lumiline 
lamps placed end to end 
conserve space. 



13 17 21 25 29 33 37 



Indirectly lighted transil- 
luminated elements of this 
character may use any type 
of translucent material, the 
choice being governed by 
the unlighted appearance, 
texture, and efficiency. 



8-36 



I E S LIGHTING HANDBOOK 



Table 8-12. Continued 



TYPE OF ELEMENT 



DIMENSIONAL 
RATIOS 





D = 0.17 W 

S = 0.30 W 

S = 1.8D 

A = (VV - C) S 



D = 0.10 W 

S = 0.20 W 

S = D 

A = WS 



S = 0.40 W 

A = 2 WS 



D = 0.36 W 

S = 0.54 W 
A = 1.43 WS 



D = 0.50 W 
S = 0.75 W 
A = 3 WS 



REFLECTANCE OR 
TRANSMITTANCE 



0.20 0.30 0.40 I 0.50 I 0.60 0.70 I 



Element Efficiency (%) 



12 15 17 19 20 21 



A graduated brightness will 
be obtained by a single 
trough located on one side; 
uniformity if lamps are 
placed at each side with 
the ratios as given. 



13 20 



26 



31 



35 



3S 



40 



With highly diffusing trans- 
lucent materials, the con- 
tour of the reflecting back- 
ground is unimportant. 
With less diffusing ma- 
terials, the shape affects the 
graduation of brightness as 
does the angle of view. 



24 35 



45 51 — — — 



Wedge-type elements use a 
polished aluminum para- 
bolic trough reflector with 
lamps centered at focus. 
The slight graduation of 
brightness (approximately 
2 to 1) with cased opal glass 
sides maintains an effective 
luminous background for 
sign letters or decorative 
patterns. 



33 



45 55 65 73 79 83 



Lamps should be centered 
on a line equidistant from 
both sides; in larger units 
the shallow cavity may be 
eliminated. 



41 55 66 



74 80 84 



86 



Lamps should be centered 
in the square cross section. 
Efficiencies apply to the 
complete element but the 
face (F) will be about 25 per 
cent brighter than the sides 
when highly diffusing ma- 
terial is used. 



LIGHTING CALCULATIONS 



8-37 



Table 8-13. Maintained Average Brightness of Various Luminous 
Elements Computed for Different Efficiencies, Areas, and Lamp 
Lumen Ratings. (Maintenance Factor Assumed to be 0.70.) 12 



LUMINOUS 


LAMP 


ELEMENT EFFICIENCY (PER CENT) 


AREA PER 




















LAMP 


Watts* 


Lumens 


20 


30 


40 


50 


60 


70 


80 


(Square Inches) 


























Footlamberts 








10 


78 


16 


24 


31 


39 


47 


55 


63 




15 


140 


28 


42 


56 


71 


85 


99 


113 




25 


258 


52 


78 


104 


130 


156 


182 


208 


100 


40 


440 


89 


133 


177 


222 


266 


310 


355 




60 


762 


154 


230 


307 


384 


461 


538 


614 




75 


1,065 


215 


322 


429 


537 


644 


751 


859 




100 


1,530 


308 


463 


617 


771 


925 


1,080 


1,234 




25 


258 


26 


39 


52 


65 


78 


91 


104 




40 


440 


44 


67 


89 


111 


133 


155 


177 




60 


762 


77 


115 


154 


192 


230 


269 


307 


200 


75 


1,065 


107 


161 


215 


268 


322 


376 


429 




100 


1,530 


154 


231 


308 


386 


463 


540 


617 




150 


2,535 


256 


383 


511- 


639 


767 


894 


1,022 




200 


3,400 


343 


514 


685 


857 


1,028 


1,200 
103 


1,371 




40 


440 


30 


44 


59 


74 


89 


118 




60 


762 


51 


77 


102 


128 


154 


179 


205 


300 


75 


1,065 


72 


107 


143 


179 


215 


250 


286 


100 


1,530 


103 


154 


206 


257 


308 


360 


411 




150 


2,535 


170 


256 


341 


426 


511 


596 


681 




200 


3,400 


228 


343 


457 


571 


685 


800 


914 




60 


762 


31 


46 


61 


77 


92 


108 


123 




75 


1,065 


43 


64 


86 


107 


129 


150 


172 




100 


1,530 


62 


93 


123 


154 


185 


216 


247 


500 


150 


2,535 


102 


153 


204 


256 


307 


358 


409 




200 


3,400 


137 


206 


274 


343 


411 


480 


548 




300 


5,520 


223 


334 


445 


556 


668 


779 


890 




500 


9,800 


395 


593 


790 


988 


1,185 


1,383 


1,581 




60 


762 


22 


33 


44 


55 


66 


77 


88 




75 


1,065 


31 


46 


61 


77 


92 


107 


123 




100 


1,530 


44 


66 


88 


110 


132 


154 


176 


700 


150 


2,535 


73 


110 


146 


183 


219 


256 


292 




200 


3,400 


98 


147 


196 


245 


294 


343 


392 




300 


5,520 


159 


238 


318 


397 


477 


556 


636 




500 


9,800 


282 


423 


564 


706 


847 


988 


1,129 




60 


762 


17 


26 


34 


43 


51 


60 


68 




75 


1,065 


24 


36 


48 


60 


72 


83 


95 




100 


1,530 


34 


51 


69 


86 


103 


120 


137 


900 


150 


2,535 


57 


85 


114 


142 


170 


199 


227 


200 


3,400 


76 


114 


152 


190 


228 


267 


305 




300 


5,520 


124 


185 


247 


309 


371 


433 


495 




500 


9,800 


220 


329 


439 


549 


659 


768 


878 




750 


14 ,550 


326 


489 


652 


815 


978 


1,141 


1,304 




100 


1,530 


21 


31 


41 


51 


62 


72 


82 




150 


2,535 


34 


51 


68 


85 


102 


119 


136 




200 


3,400 


46 


69 


91 


114 


137 


160 


183 


1 ,500 


300 


5,520 


74 


111 


148 


185 


223 


260 


297 




500 


9,800 


132 


198 


263 


329 


395 


461 


527 




750 


14 ,550 


196 


293 


391 


489 


587 


684 


782 




1,000 


20 ,700 


278 


417 


556 


696 


835 


974 


1,113 



' Incandescent lamp watts. 



8-38 



I E S LIGHTING HANDBOOK 



Illumination at a Specific Location 

The methods described for determining average illumination in large 
areas do not give accurate values at specific locations. If it is desired to 
know the illumination at specific points, calculations are made "point-by- 
point." 

Calculations with point sources. To determine the illumination at definite 
points in installations where (1) there is little reflection of light from the 
surroundings, and (2) where the distance from the source is large compared 
to the source size, variations of the inverse square law are used in all 
point-by -point calculations involving relatively small sources. In such 
situations the illumination is proportional to the intensity of the source 
and inversely proportional to the square of the distance from the 



source 



.14, 15, 16 



D 2 
where E n = the illumination normal to the light 

rays( footcandles) 
I = intensity (candlepower) 
D = the distance (feet) 

See Fig. 8-8a. When the distance from the source to the point of 
measurement is at least five times the maximum dimension of the source, 
the inverse square law ordinarily can be used with acceptable accuracy. 

The deviation from the inverse square law produced by large sources is 
discussed on pages 8-41 and 8-44. 

Lambert's cosine law of illumination. If the surface on which the illum- 
ination to be determined is tilted, instead of normal to the rays, the light 
will be spread over a greater area, reducing the illumination in the ratio 
of the area of plane A to the area of plane B, as shown in Fig. 8-8b. This 
ratio is equal to the cosine of the angle of incidence or tilt and: 



where 



E = — cos 6 
D 2 

6= angle of incidence 




ILLUMINATION E = 
FLUX IN LUMENS(F.) 




AREA OF PLANE B = 



■cose 



cos e 



FIG. 8-8. Point-by-point calculations assume a point source and involve applica- 
tions of the inverse square and cosine laws. 



LIGHTING CALCULATIONS 



8-39 



Referring to Fig. 8-9, E n is the 
illumination at point p on a plane 
normal to the ray from the light 
source ; E h is the illumination at 
point p on a horizontal surface; 
E v is the illumination at point p 
on a vertical surface; h is the 
vertical mounting height of the 
light source above the point p; 
I is the horizontal distance from 
the light source to the point p; 
d is the actual distance from the 
light source to the point p; I p is 
the candlepower of the light 
source in the direction of the 
point p (from the distribution 
curve). 6h is the angle of inci- 
dence for horizontal illumination, 
8 V is the angle of incidence for 
vertical illumination 



^ 




*$$P 



[* HORIZONTAL DISTANCE^ 
FROM POINT, I 

FIG. 8-9. Diagram for point-by-point calcu- 
-rjn-i , 7 lations showing candlepower distribution curve 
and other variables. 



and / are known, the angle of in- ' 
cidence may be obtained from the nomogram, Appendix Fig. A-2. 
The equations may be expressed in terms of either h or a 1 : 21 



E„ = — COS h = -75 

h 2 d 2 

I 3 / 

Eh = -r-; cos dh = -rr a cos 9 h 
h 1 d 2 



d = 



h 



Cosd h 
Cos 6 V = sin dh 



E v = — cos" d h sin 6 h 
h 2 



I ■ 3, / 

— sm 6 h = — cos V 
d z a 2 



To determine the cumulative horizontal illumination at point p from 
several contributing luminaires, it is desirable to proceed along a definite 
pattern. 22 Table 8-14 is a convenient form for point-by-point calculations; 
the candlepower values shown are initial values from Fig. 8-9. Although 
the illustrations used are for horizontal planes, the same procedure may be 
used for calculating illumination on a vertical plane by using values of 
d, h, and obtained by rotating the candlepower distribution curve in 
Fig. 8-9, 90 degrees in a clockwise direction. 

It is more convenient to obtain the illumination from tables. In table 
8-15, footcandles on a horizontal plane have been calculated from the 
formula 



E h 



d 2 C ° Sdh 



Conversion charts can also be employed, 2 



8-40 



I E S LIGHTING HANDBOOK 



Asymmetrical distribution. When point-by-point calculations are to 
be made for luminaires having an asymmetric candlepower distribution, 
a group of distribution curves must be available. A practical way of 
presenting a group of curves for a typical asymmetrical luminaire is shown 
in Fig. 8-10. 




30 40 50 60 

ANGLE IN LATERAL PLANE, e L , IN DEGREES 



FIG. 8-10. Candlepower at various vertical and horizontal angles from a luminaire 
with as3 r mmetric distribution. 

Table 8-14. Form for Point-by-Point Calculations of Initial Illumination 
at Several Points Along a Horizontal Plane 



1 


h 


l 
h 


6* 


cp\ 


cos 3 0J 


cp X COS 3 


ir- 


Eh 





30 








12,600 


1.00 


12,600 


900 


14.0 


5 


30 


0.167 


9.5 


12,600 


0.960 


12,100 


900 


13.5 


10 


30 


0.333 


18.4 


11,800 


0.856 


10,100 


900 


11.2 


15 


30 


0.500 


26.6 


8,600 


0.718 


6,180 


900 


6.9 


20 


30 


0.666 


33.7 


5,000 


0.576 


2,880 


900 


3.2 


25 


30 


0.834 


40.0 


2,000 


0.450 


900 


900 


1.0 


30 


30 


1.00 


45.0 


1,700 


0.355 


602 


900 


0.67 


35 


30 


1.16 


49.3 


1,300 


0.275 


360 


900 


0.40 


40 


30 


1.33 


53.1 


800 


0.215 


172 


900 


0.19 


45 


30 


1.50 


56.4 


600 


0.170 


102 


900 


0.11 



* From Appendix Figure A-2, page A-45. 

t From Fig. 8-9. 

j From Appendix Table 25, page A-39. 



LIGHTING CALCULATIONS 



8-41 



Calculations with line sources. 25 For a perfectly diffusing line source, 
the candlepower at any angle in the plane containing the source axis is 
approximately equal to the maximum candlepower times the cosine of the 
angle. This relationship is reasonably accurate for fluorescent lamps and 
other sources where the diameters are small compared to the length. 
_ The formulas most frequently used for calculations involving a perfectly 
diffusing line source are: 

F = 7T 2 T 

J. u J. max 

where F = flux (lumens) emitted per unit length 

I max = maximum candlepower 

and E = L = IXA 

2d 2d 

where E = illumination on a plane parallel to the source 

d = distance from source to plane (feet) 
B = brightness (footlamberts) 
F = total flux (lumens) 
A = area (square feet) 

The lumen output of fluorescent lamps divided by the maximum candle- 
power is somewhat lower than t 2 because the emission is not completely 
diffuse. For 15- to 100-watt preheat-starting fluorescent lamps the range is 
9.15 to 9.30, with an average value of 9.25. 25 

It will be noted that the illumination from a line source of infinite length 
varies inversely as the distance but not inversely as the square of the dist- 
ance. Figure 8-12 illustrates the relationship for a 4-foot line source. 2 




3 4 5 6 

SOURCE-PLANE DISTANCE IN FEET 



FIG. 8-11. Average illumination produced on parallel planes at various distances 
from a diffuse line source of a length equal to or greater than the distance varies in- 
versely as the distance. As the distance exceeds the length of the source, the rela- 
tionship approaches the inverse -square-law condition characteristic of point sources. 



8-42 



I E S LIGHTING HANDBOOK 



Table 8-15. Initial Illumination Computed for Points at Various Loca- 
tions on a Horizontal Plane in Terms of 100 and 
100,000 Candlepower Sources* 12 
100 CANDLEPOWER SOURCE 



HORIZONTAL DISTANCE FROM UNIT (feet) 










1 


2 


3 


4 


5 


6 


7 


8 

63° 
.559 


9 


10 

6S° 
.320 


15 


20 


30 




4 


e 0' 
6.250 


14° 
5.707 


27° 
4.472 


37° 
3.200 


45° 
2.210 


51° 
1.524 


56° 
1.066 


60° 
.764 


66° 
.41! 


75° 
.107 


79° 
.047 


82° 
.015 




5 


0°0' 
4.000 


11° 
3.771 


22° 
3.202 


31° 

2.522 


39° 

1.904 


45° 

1.414 


50° 
1.050 


54° 

.785 


58° 
.595 


61° 
.455 


63° 

.358 


72° 
.126 


76° 
.057 


81° 
.017 




6 


0°0' 

2.778 


9° 
2.673 


18° 
2.372 


27° 
1.9S7 


34° 

1 . 60! 


40° 
1.260 


45° 

.982 


49° 
.766 


53° 

-.600 


56° 

.474 


59° 
.378 


68° 
.142 


73° 
.066 


79° 
.021 




7 


0°0' 
2.041 


8° 
1.980 


16° 
1.814 


23° 
1.585 


30° 
1.336 


36° 

1.100 


41° 
.893 


45° 

.722 


49° 
.583 


52° 

.47.' 


55° 

.385 


65° 
.154 


71° 
.074 


77° 
.024 




8 


0°0' 
1.563 


7° 
1.527 


14° 
1.427 


21° 

1.283 


27° 
1.1 If 


32° 
.953 


37° 
.800 


41° 

.640 


45° 

.552 


48° 
.45: 


51° 
.3S1 


62° 
.163 


68° 
.080 


75° 
.026 


H 


9 


0°0' 
1.235 


6° 
1.212 


13° 
1.148 


18° 
1.054 


24° 
.94: 


29° 
.825 


34° 
.711 


38° 
.607 


42° 
.515 


45° 
.43- 


48° 
.370 


59° 
.168 


66° 
.085 


73° 
.029 


.fa 
1 


10 


0°0' 
1.000 


5°43' 
.985 


11° 
.943 


17° 
.879 


22° 

.so; 


27° 
.716 


31° 
.631 


35° 

.550 


39° 

.476 


42 s 

.41 


45° 

.354 


56° 

.171 


63° 

.0S9 


72° 
.032 




12 


0°0' 

.694 


4°46' 
.687 


9" 
.668 


14° 
.634 


18" 

.59: 


23° 

.546 


27° 
.497 


30° 

.448 


34° 

.400 


37° 
.35 


40° 
.315 


51° 
.169 


59° 

.094 


68° 
.036 


o 

!3 


14 
16 


0°0' 
.510 


4°5' 
.506 


8° 
.495 


12° 

.477 


16° 
.45' 


20° 

.426 


23° 
.396 


27° 
.365 


30° 
.334 


33° 

.30 


36° 

.275 


47° 
.162 


55° 

.096 


65° 
.039 


pa 
o 


0°0' 
.391 


3°35' 

.38S 


7° 
.382 


11° 

.371 


14° 
.35; 


17° 
.339 


21° 
.321 


24° 
.300 


27° 
.280 


29° 
.25 


32° 
.238 


43° 

.152 


51° 

.095 


62° 
.041 


< 


18 


C 0' 
.309 


3°H' 
.307 


6° 
.303 


9° 
.297 


13° 
.28; 


16° 
.276 


18° 
.264 


21° 
.250 


24° 
.236 


27° 
.22 


29° 
.206 


40° 
.140 


48° 
.092 


59° 
.042 




20 


0°0' 

.250 


2°51' 
.249 


5°43' 
.246 


9° 
.242 


11" 

.23( 


14° 
.228 


17° 
.219 


19° 
.210 


22° 
.200 


24° 

.191 


27° 
.179 


37° 

.128 


45° 

.088 


56" 
.043 


> 

O 

35 


22 


0°0' 
.207 


2°36' 
.206 


5°10' 
.205 


8° 
.201 


10° 
.19( 


13° 

.192 


15° 
.185 


18° 
.179 


20° 

.171 


22° 

.16 


25° 
.155 


34° 

.114 


42° 
.084 


54° 
.043 


•< 

W 

a 


24 


0°0' 
.174 


2°23' 
.173 


4°45' 
.172 


7° 
.170 


10° 

.161 


12° 

.163 


14° 
.158 


16° 
.154 


18° 
.148 


21° 
.14 


23° 

.137 


32° 

.106 


40° 
.079 


51° 
.042 


t3 

o 

CO 


25 


0°0' 
.160 


2°17' 
.160 


4°34' 

.15S 


7° 
.157 


9° 
.154 


11° 
.151 


14° 

.147 


16° 

.143 


18" 

.138 


20° 
.13 


22° 
.128 


31° 

.101 


39° 
.076 


50° 
.042 


a 


30 


0°0' 
.111 


1°54' 
.111 


3°50' 
.111 


5°43' 
.109 


8° 
.108 


9° 
.107 


11° 
.105 


13° 
.103 


15° 
.100 


17° 
.09: 


18° 
.095 


27° 
.OSO 


34° 
.064 


45° 
.039 


O 


36 


0"0' 
.077 


1°36' 
.077 


3°ir 

.077 


4*46' 
.076 


6° 

.076 


S° 
.075 


9° 
.074 


11° 
.073 


13° 

.072 


14° 

.071 


16° 

.069 


23° 
.061 


29° 
.052 


40° 
.035 




40 


0°0' 
.063 


1°26' 
.062 


2°52' 
.062 


4°17' 
.062 


5°43' 
.062 


7° 
.061 


9° 
.050 


10° 

.060 


11° 
.059 


13° 
.05. 


14° 
.057 


21° 

.051 


27° 
.045 


37° 
.032 


w 


50 


0°0' 
.040 


1°9' 
.040 


2°17' 
.040 


3°26' 
.040 


4°34' 
.040 


5°43' 
.039 


7° 
.039 


8° 
.039 


9° 
.039 


10° 

.03; 


11° 
.038 


16° 
.035 


22° 
.032 


31° 
.025 




00 


0°0' 
.028 


0°57' 
.028 


1°55' 
.028 


2°52' 
.02S 


3°50' 
.028 


4°46' 
.027 


5°43' 
.027 


.027 


8° 
.027 


9° 

.02; 


9° 
.027 


14° 

.025 


18° 
.024 


27° 
.020 




100,000 CANDLEPOWER SOURCE 




100 


0°0' 
10.000 


0°34' 

9.999 


1°9' 
9.994 


1°43' 
9.987 


2°17' 

9.976 


2°52' 
9.963 


3°26' 
9.946 


4°0' 
9.927 


4°34' 
9.905 


5°9' 

9.8S0 


5°43' 

9.852 


9° 
9.660 


11° 
9.439 


16° 
8.S19 




150 


0°0' 
4.444 


0°23' 
4.444 


0°46' 
4.443 


1°9' 
4.442 


1°32' 
4.440 


1°55' 
4.437 


2°17' 
4.434 


2°40' 
4.430 


3°2' 
4.421 


3°26' 
4.416 


3°49' 
4.415 


5°43' 
4.379 


8° 
4.324 


11° 
4.195 




200 


0"0' 
2.500 


0°17' 
2.500 


0°34' 
2.500 


0°52' 
2.499 


1°9' 
2.499 


1°26' 
2.498 


1°43' 

2.497 


2°0' 
2.495 


2°17' 
2.494 


2°35' 
2.492 


2°52' 
2.490 


4°17' 
2.479 


5°43' 
2.463 


9° 
2.415 



* Uoper figures — angle between light ray and vertical. Lower figures— footcandles on a horizontal plane 
produced by source. 



LIGHTING CALCULATIONS 



8-43 



Brightness of preheat-star ting -type fluorescent lamps. The average 
brightness — B a integrated across the diameter in the center of fluorescent 
lamps may be calculated by the formula: 27 



B e 



K X Ft 



9.25 X D X L 



where 



B a = 



K = 



Ft = 
D = 
L = 



average brightness (in cp/sq in. ; 1 cp per 
sq in. = 452 footlamberts) 
ratio, brightness of center section to av- 
erage brightness (K = 1.09 for 20-, 30-, 
40-, and 100-watt lamps) 
total lumen output 
diameter (inches) 
luminous length (inches) 



The approximate brightness B 6 of a fluorescent lamp at any angle with 
the lamp axis is: 



where 



Be = 

Be 
Ft 
Ke 

D 
L 



Ft 



K e X D X L X sin 6 



brightness at any angle 6 (candles/sq in.) 

total lumen output 

the ratio of lamp lumens to candlepower at 

various angles (see Table 8-16) 

diameter (inches) 

luminous length (inches) 

angle of observation 



Table 8-16. Values at Various Angles of the Lamp-Lumen: Candlepower 
Ratio K e for Preheat-Starting Types of Fluorescent Lamps* 



ANGLE 


*0 


Sin 9 


0° 








10° 


172 


.174 


20° 


46 


.342 


30° 


24.7 


.500 


40° 


17.1 


.643 


50° 


13.3 


.766 


60° 


11.3 


.866 


70° 


10.1 


.940 


80° 


9.5 


.985 


90° 


9.25 


1.000 



* Average for 15-, 20-, 30-, 40- and 100-watt lamps. 



8-44 



I E S LIGHTING HANDBOOK 



Calculations with surface sources. 24 ' 28 ' 29 An infinitely large plane source 
radiating light to a parallel work plane produces an illumination level: 29 

E = B s 

where B s — source brightness (footlamberts). 

with such a source (large skylight or uniformly bright ceiling in large 
room), the illumination is seen to be independent of the distance. 

Figures 8-12, 8-13, and 8-14 provide data on several common types of 
luminaires. 



60-WATT INCANDESCENT LAMP 



TWO 15-WATT FLUORESCENT LAMPS 




FIG. 8-12. Illumination produced by various reflector and lamp combinations at 
different distances from the illuminated plane. (Approximate) 




SIDE VIEW 



I MOUNTING 
i HEIGHT 

j in feet: 




10 12 14 16 2 4 6 8 

DISTANCE IN FEET FROM CENTER OF UNIT 



FIG. 8-13. Illumination distribution curves for a closed-end R.L.M. type fluores- 
cent luminaire (two 40-watt white preheat-starting-type fluorescent lamps) at vari- 
ous mounting heights. (Based on output of 2,100 lumens per lamp) 



LIGHTING CALCULATIONS 



8-45 



100 

80 
60 

40 



< 100 

z 

2 



ONE LAMP IN REFLECTOR 3 FT LONG 





a 








<*»-L---*ViA 


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L B=7 2/ 3 IN. 


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FOUR LAMPS IN REFLECTOR 12 FT LONG 

100 



A = S 7 /q IN. 
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^ 


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ONE LAMP IN REFLECTOR 4 FT LONG 



THREE LAMPS IN REFLECTOR 12 FT LONG 



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60 



A = 6 IN. 
L = 4 FT 




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DISTANCE, D, IN FEET FROM CENTER OF REFLECTOR 

FIG. 8-14. Illumination produced by various sizes and lengths of reflectors for 
fluorescent lamps ; a and b are for a parabolic aluminum reflector of | -inch focal length 
with a T-8 lamp producing 460 lumens per foot; c and d are for a similar reflector of 
li-inch focal length with a T-12 lamp producing 500 lumens per foot. 

For relatively small circular sources, when the distance to the point at 
which the illumination is to be determined is large compared to the source 
dimensions, the inverse square law can be applied. For closer points the 
illumination at points along the axis of the disk is: 



E = 



where 



F = lumen output of disk (brightness in 
f ootlamberts times area) 

d = the distance from point on axis to the 
edge of the disk. 

The formula assumes a cosine distribution and the distribution of many 
direct-lighting luminaires approximate this. The illumination at points 
along the axis can also be calculated by considering the circular source as a 
portion of the infinite plane, in which case: 



where 



E = BsX sin 2 

E = illumination (footcandles) 
B s = source brightness (f ootlamberts) 
8 — angle, from the point on the axis formed 
by axis and line to the edge of the disk. 



8-46 



I E S LIGHTING HANDBOOK 



For very close points the disk approaches an infinite plane and the formula 
on page 8-44 would apply. Either of these formulas may be used to 
determine the illumination at points along the axis of an annular or ring 
source by rinding the illumination from the whole disk and that from the 
"hole" and then subtracting the latter from the former. 

The curves of Fig. 8-15 and Fig. 8-16 relate the average brightness (foot- 
lamberts) of a rectangular luminous area such as a panel, window, or wall, 
the angles with their apexes at a given point subtended by the area, and 
the illumination at the point produced by the area. 14 The contribution 
of each such luminous area to the illumination at a given point is calculated 
independently. Values of illumination E at points in planes parallel or 
perpendicular to rectangular luminous areas may be obtained bv sub- 

(E\ 

stituting the brightness B ot the area and the ratio I - ) from Fig. 8-15 or 

(E\ W 

8-16) in the following equation: E = B X I „ ) 

Other methods also have been developed for calculating the illumination 
from the sun and sky. 31 




10 20 30 40 50 60 70 80 90 
ANGLE 0, IN DEGREES 

FIG. 8-15. The ratio of illumination E 
(at the point P of intersection of a per- 
pendicular erected at one corner of a 
rectangular luminous area and a parallel 
illuminated plane) to the brightness B 
of the luminous area is a function of the 
angles B and 6 with their apexes at the 
point of intersection, subtended by the 
rectangle sides intersecting the perpendic- 
ular. 



20 30 40 50 60 70 80 90 
ANGLE 0. IN DEGREES 

FIG. 8-16. Ratio of the illumination 
E (at a point P in a line perpendicular to 
one corner of a rectangular luminous 
area, which with the base of the rectangle 
forms the illuminated plane) to the bright- 
ness B of the luminous area is a function of 
the angles B and 6 with their apexes at 
the point of intersection, subtended by 
the rectangle sides intersecting the per- 
pendicular. 



LIGHTING CALCULATIONS 



8-47 



Street Lighting 

Computations made in designing a street-lighting installation involve 
both point-by-point and average-flux methods of calculation. 33 

Basic photometric data. The fundamental photometric data with which 
spacing-mounting height relationships and utilization efficiencies of specific 
luminaires can be determined are given in isocandle curves. These data, 
together with application information, are available from manufacturers. 

Isocandle curves. Figure 8-17 shows an isocandle diagram for a typical 
street-lighting luminaire. The curves represent the loci of points of 
intersection of rays of equal candlepower striking a spherical surface around 
the luminaire. As the curves of even an asymmetric luminaire are usually 
symmetrical on either side of the vertical plane at right angles to the 
curb line, only one hemisphere is usually necessary to show the distribution. 




FIG. 8-17. Isocandle diagram for typical street lighting luminaire. 

Candlepower distribution curves. Most modern street-lighting luminaires 
produce an asymmetrical distribution of light directed in two main beams 
up and down the roadway. Distribution curves are customarily shown 
in the vertical and horizontal planes as in Fig. 8-18. 



110° 


130° 150° 180° I50 c 


130° 




110' 




/\ \ " / 










/ \house side/ 








90° >»— 










20° 






yf$f 












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^\ 




Jr\ 


o/ 


o^ 


//?0o 








£>/ 




\* 


"T^ STREET SIDE' 


\ • 




s*7 



130° 150° 180° 150° I30 c 



II0 C 



30° 30° 

HORIZONTAL DISTRIBUTION 



50 c 



90 ° I rA 


0f] 90° 




S?7te^L_ 1 




vP /rP^C^J 


^\~S/ A~ 


\ / \*7 



30° 30° 

VERTICAL DISTRIBUTION 

("PLANE PARALLEL TO STREET) 



FIG. 8-18. Candlepower distribution curves for asymmetrical street-lighting 
luminaire. 



8-48 



I E S LIGHTING HANDBOOK 



The vertical distribution curve represents the candlepower emitted from 
the luminaire at various angles in a vertical plane which passes through 
the luminaire axis and the maximum candlepower viewed from the side. 
If the luminaire is asymmetrical, these will be two vertical planes. The 
horizontal distribution curve shows the candlepower emitted by the 
luminaire at specific angles in a horizontal cone through the maximum 
candlepower as viewed from the top. 

The two curves, vertical and horizontal, through the maximum beams 
of the luminaire give a fairly accurate picture of the light distribution of a 
particular luminaire. For a more complete record an entire set of vertical 
and horizontal distribution curves must be obtained, with the angular 
interval between curves small enough to permit accurate interpolation. 
In practice, the isocandle curves are employed. 

Luminaire application data. The actual 
performance of particular luminaires at de- 
finite spacings and mounting heights in pro- 
ducing illumination on the street (or the 
location of units to achieve specified levels) 
is calculated from the basic photometric 
data. Application information is presented 
in three forms! The utilization curve, gen- 
eral isolux curves for a single luminaire, and 
accumulative isolux curves for two or more 
luminaires under a specific set of conditions. 
Utilization curves. Figure 8-19 shows 
utilization curves for a type III luminaire 
(see page 13-35). Since the luminaire di- 
rects two main beams up and down the street 
with a greater amount of light directed to- 
ward the street side, one curve gives the in- 
tegrated portion of light which intersects 
areas on the house side and the other curve 
shows the integrated portion on the street 
side, expressed in per cent of the total gen- 
erated light. 

















STREET 
SIDE 


















• HOUSE 
SIDE 
















RAT 


2 3 4 5 
WIDTH OF AREA 



o 

t- 0.2 



t 0.1 

UJ 

o 
o 




MOUNTING HEIGHT 

FIG. 8-19. Utilization curves 
for a type III street-lighting 
luminaire showing per cent of 
total lumen output falling on 
street and house sides of the 
vertical axis. 



The formulas used are: 



Lamp lumens X coefficient of utilization 
Spacing* X width of pavement 

Area X average initial illumination 
Coefficient of utilization 

In addition to calculating average illumination, the utilization chart is 
also effective in determining the width of the street for which a given design 
is applicable. 



Average initial illumination = 



Required lamp lumens = 



* Spacing is measured along centerline of street. 
tive lumens. 



When luminaires are opposite, double the value of effec- 



LIGHTING CALCULATIONS 



8-49 



MULTIPLY BY 
FOR CORREC- 

MOUNTING TION 

HEIGHT FACTOR 



General isolux curves. Isolux curves indicate the amount of light striking 
the road surface from a single unit or from a number of units. All 
points on a given isolux line receive the same horizontal illumination. 

Isolux curves for a single 
luminaire can be made up for 
some specific mounting height 
with the horizontal distances 
shown (1) in feet, or (2) ex- 
pressed as ratios of the actual 
distance to the mounting 
height, as in Fig. 8-20. To 
correct this type of curve for a 
different mounting height, the 
footcandle values are multi- 
plied by the conversion factor 
given. This factor is the ratio 
of the present or stated mount- 
ing height squared, to. the new 
mounting height squared. 

To determine the illumina- 
tion in the horizontal plane at 
a given point from the second 
type of isolux curve (Fig. 8-20), 
locate the point in question and 
express its distance from a 
point directly under the lumi- 
naire in terms of the mounting 
height, which in this case is 
25 feet. For example, the m- 




1 O I" 2 3 

RATIO OF LATERAL DISTANCE TO MOUNTING HEIGHT 



FIG. 8-20. Isolux curves for a street-light- 
ing luminaire plotted for ratios of lateral and 
longitudinal distances to mounting height; 
the curves shown are for a 25-foot mounting 
tersection of the lateral line height. 
1 and the longitudinal line 2 

is a point on the street 50 feet from the luminaire) measured along 
the curb line) and 25 feet 
from the curb toward the center 
of the street. The illumina- 
tion at this point, from the 
curves, is 0.3 footcandle. 
Accumidative isolux curves. 
When two or more lumi- 
naires are being considered as 
in a typical installation, the 
illumination is expressed by 
lines representing the accumu- 
lative effect of all the lumi- FIG . 8 . 2L The isolux curves shown here 
naires. _ Such a curve is lllus- indicate the cumulative effect of two adjacent 
trated m Fig. 8-21. street-lighting luminaires. 




30 40 50 60 
DISTANCE IN FEET 



8-50 



I E S LIGHTING HANDBOOK 
REFERENCES 



1. Sturrock, W., "Levels of Illumination," Mag. of Light, No. 4, 1945. 

2. Harrison, W., and Anderson, E. A., "Coefficients of Utilization," Trans. Ilium. Eng. Soc, March 1920. 

3. Moon, P., and Spencer, D. E^ "Maintenance Factors," Ilium. Eng., March, 1946. Gaetjens, A. K., 
"A Guide to Realistic Maintenance Factors," Ilium. Eng., May, 1945. 

4. Data/or Designing Interior Illumination, Folder A-4854, Lamp Division, Westinghouse Electric Corpora- 
tion, Bloomfield, New Jersey, October, 1946. 

5. Amick, C. L., Fluorescent Lighting Manual, McGraw-Hill Book Company, Inc., New York, 1947. 

6. I.E.S. Committee on Quality and Quantity of Illumination "Report No. 3," Ilium. Eng., May, 1946. 

7. Buckley, H., "On Radiation from the Inside of a Circular Cylinder," Philosophical Magazine, October 
1927, September 192S, and March, 1934. 

8. Hisano, K., "Light Flux Distribution in a Rectangular Parallelepiped and its Simplifying Scale " 
Ilium. Eng., March, 1946. 

9. Yamauti, Z., "Recherche d'un Radiateur Integral au moyen d'un Corps Cylindrique," Com. Int. 
des Poids et Mes., Proc. Verb, 1933. 

10. Moon, P., "Interreflections in Finite Cylinders," J. Optical Soc. Am., January and March, 1941. Moon, 
P., "Interreflections in Rooms," J. Optical Soc. Am., January, June, and July, 1946. Moon, P., and Spencer, 
D. E., "Light Distributions in Rooms," J. Franklin Inst. August, 1946. 

11. Essential Data for General Lighting Design, Folder D, Lamp Department, General Electric Company, 
Cleveland, Ohio, May, 1944. 

12. Harrison, W., and Weitz.C.E., Illumination Design Data, Bulletin LD-6A, Lamp Department, General 
Electric Company, Cleveland, Ohio, October, 1936. 

13. Reinhardt, H., Fluorescent Lighting Handbook, Hygrade Lamp Division, Hygrade Sylvania Corpora- 
tion, Salem, Massachusetts, 1942. 

14. Moon, P., Scientific Basis of Illuminating Engineering, McGraw-Hill Book Company, Inc., New York, 
1936. 

15. Kraehenbuehl, J. O., Electrical Illumination, John Wiley & Sons, Inc., New York, 1942. 

16. Higbie, H. H., Lighting Calculations, John Wiley & Sons, Inc., New York, 1934. 

17. Boast, W. B., Illumination Engineering, McGraw-Hill Book Company, Inc., New York, 1942. 

18. Barrows, W. E., Light, Photometry and Illuminating Engineering, McGraw-Hill Book Company, Inc., 
New York, 1938. 

ILLUMINATION FROM PROJECTED BEAMS 

19. Hallman, E. B., "Floodlighting Design Procedure as Applied to Modern Setback Construction," Trans. 
Ilium. Eng. Soc, April, 1934. Dearborn, R. L., "Floodlighting Design by Graphical Method," Ilium. Eng., 
September, 1945. 

STORE AND SIGN LIGHTING 

20. Ketch, J. M., Three A's of Store Lighting, Bulletin LD-7, Lamp Department, General Electric Com- 
pany, Cleveland, Ohio, April, 1946. Lighting Handbook, Lamp Division, Westinghouse Electric Corporation- 
Bloomfield, New Jersey, 1947. 

ILLUMINATION FROM POINT SOURCES 

21. Goodbar, I., "Shortcut Method of Point by Point Calculations," Ilium. Eng., January, 1946. 

22. See reference No. 15, page 235, No. 16, pages 107, 115, and 303. 

23. See reference No. 17, pages 54, 71, 94, and 97. 

24. Franck, K., "Illumination Conversion Chart for Inclined Work Planes," Ilium. Eng., April, 1944. 

ILLUMINATION FROM LINE SOURCES 

25. Spencer, D. E., "Exact and Approximate Formulae for Illumination from Troffers," Ilium. Eng., 
November, 1942. Wakefield, E. H., and McCord, C, "Discussion of Illumination Distribution from Linear 
Strip and Surface Sources," Ilium. Eng., December, 1941. Wakefield, E. H., "A Simple Graphical Method 
of Finding Illumination Values from Tubular, Ribbon, and Surface Sources," Ilium. Eng., February, 1940. 
Wohlauer, A. A., "The Flux from Lines of Light," Trans. Ilium. Eng. Soc, July, 1936. Whipple, R. R., 
'Rapid Computation of Illumination from Certain Line Sources," Trans. Ilium. Eng. Soc, June, 1935. 

26. Baugartner, G. R., "Practical Photometry of Fluorescent Lamps and Reflectors," Ilium. Eng., De- 
cember, 1941. 

27. Reinhardt, H., "Illumination from a Line Source," Elec World, December, 1945. 

28. Linsday, E. A., "Brightness of Cylindrical Fluorescent Sources," Ilium. Eng., January, 1944. 

ILLUMINATION FROM SURFACE SOURCES 

29. Benford, Frank, "Graphics in Engineering," Ilium. Eng., July, 1945. Spencer, D. E., "Calculation 
of Illumination from Triangular Sources," J . Optical Soc. Am., May, 1942. Higbie, H. H., "Prediction of 
Illumination at a Point from Sources of Any Shape," Ilium. Eng., January, 1941. Greenberg, B. F., "A De- 
vice for the Determination of Illumination," Ilium. Eng., July, 1940. Cherry, V. H., Davis, D. D., and Boel- 
ter, L. M. K., "A Mechanical Integrator for the Determination of the Illumination from Diffuse Surface 
Sources," Trans. Ilium. Eng. Soc, November, 1939. Higbie, H. H., "Illumination Distribution from Surface 
Sources in Rooms," Trans. Ilium. Eng. Soc, February, 1936. Higbie, H. H., and Bychinsky, W. A., "Il- 
lumination Distribution Measurements from Surface Sources in Sidewalls," Trans. Ilium. Eng. Soc, March, 
1934. 

30. See reference No. 16, pages 107 and 10S. 

31. See reference No. 15, pages 264-273. 

ILLUMINATION FROM SUN AND SKY 

32. Moon, P., and Spencer, D. E., "Illumination from a Non-Uniform Sky," Ilium. Eng., December, 
1942. Elvegard, E., and Sjostedt, G., "Calculation of the Spectral Energy Distribution in Sunlight and 
Skylight," Ilium. Eng., July, 1941. Elvegard, E., and Sjostedt, G., "The Calculation of Illumination from 
Sun and Sky," Ilium. Eng., April, 1940. Daniels, J., "Light and Architecture," Trans. Ilium. Eng. Soc, 
April, 1932. Higbie, H. H., and Turner-Szymanowski, W., "Calculation of Dayiighting and Indirect Arti- 
ficial Lighting by Protractor Method," Trans. Ilium. Eng Soc, March, 1930. Bull, H. S., "A Nomogram 
to Facilitate Daylight Calculations," Trans. Ilium. Eng. Soc, May, 1928. Brown, VV. S., "Practical Daylight 
Calculations for Vertical Windows," Trans. Ilium. Eng. Soc, March, 1926. I.E.S. Committee on Sky Bright- 
ness, "Daylight Illumination on Horizontal, Vertical and Sloping Surfaces," Trans. Ilium. Eng. Soc, May, 
1923. 

STREET LIGHTING CALCULATIONS 

33. Dean, J. H., "A Graphical Method of Computing Street Lighting Illumination Charts," Ilium. Eng., 
July, 1942. Westinghouse Street Lighting Engineering Handbook, Lighting Division, Westinghouse Electric 
Corporation, Cleveland, Ohio, 1946. Stahle, C. J., Electric Street Lighting, John Wiley & Sons, Inc., New York 
1929. 

34. Merrill, G. S., and Prideaux, G. F., "Nomogram for Blackout Lighting Calculations," Ilium. Eng. 
March, 1942. 



SECTION 9 
DAYLIGHTING 



As a consequence of evolution, human beings are adapted to the char- 
acteristics of daylight illumination . These characteristics vary over a wide 
range: At noon on a clear day with the sun directly overhead (possible 
only in latitudes within about 23 degrees of the equator) as high as 10,000 
footcandles may be available on a horizontal plane. Clear sky alone can 
provide more than 1,500 footcandles and a clouded sky may produce 4,000 
footcandles. Full moonlight provides about 0.02 footcandle. 

Figure 9-1 shows the seasonal and daily variations in average daylight 
illumination characteristic of locations lying along 42 degrees north latitude 
(Boston, Cleveland, Chicago, Rome, or Barcelona). Locations closer to 
the equator usually will receive more illumination and those closer to the 
poles less. The number of clear and cloudy days which may be expected 
each year in a given area may be obtained from the United States Weather 
Bureau. 

Duration of Sunlight on Architectural Surfaces 

Neglecting local obstructions (hills, trees, buildings, clouds, etc.), the 
time during which sunlight will be incident on horizontal surfaces at a 
given latitude corresponds with the hours between sunset and sunrise for 
that latitude. 

For sloping surfaces, the duration of sunlight incidence equals the sun- 
rise to sunset period for a latitude equal to the local latitude plus (for 
north-facing slopes) or minus (for south-facing slopes) the slope angle 
measured down from the horizontal. 

Sunlight will strike vertical surfaces during the sunrise to sunset hours 
in which the sun's azimuth is greater than 6 — 90 degrees and less than 
6 + 90 degrees. (6 is the angle between a normal to the vertical surface 
and true south.) 

Window Design 

Through well-designed and regularly cleaned skylights, windows, doors, 
and glass-block wall areas, useful quantities of daylight may be provided in 
buildings. For most purposes, the higher the daylight illumination level 
in a building the better, providing the illumination is uniformly distributed 
and the brightness ratios are within comfortable limits. 

It is recommended that windowed buildings be designed so that a day- 
light illumination level of at least 10 footcandles will be provided over the 
entire horizontal working plane. In the northern hemisphere a sky bright- 
ness representative of conditions encountered at eight o'clock in the morn- 
ing on a December twenty-first with cloudy sky is a common basis for 
design. 



Note: References are listed at the end of each section. 



9-2 



I E S LIGHTING HANDBOOK 



The international standard of sky brightness (5,000 lux, or 465 footlam- 
berts) is of the same order of magnitude as that of cloudy December morn- 
ing skies likely to be observed in the northern United States. 

Using this value and Figs. 8-15 and 8-16, the minimum daylight il- 
lumination likely to be provided at any point on a horizontal plane by 
rectangular window or skylight openings may be determined. 

Design factors. Because windows absorb some light when clean and 
more when dirty, the values obtained from Figs. 8-15 and 8-16 should be 
multiplied by an efficiency and a maintenance factor. 





APPARENT SOLAR 
TIME* INI HOURS 


ALTITUDE 
OF SUN 


ILLUMINATION IN FOOTCANDLES 


+ 


BEFORE OR AFTER 
NOON 


ABOVE 

HORIZON 

IN DEGREES 


SUN 


ONLY 


CLEAR SKY 
ONLY 


CLOUDY SKY 
ONLY 




























-100 




















7 






























■5 






•7 








-1000 




-100 
















-4 






•6 






-10 




-2000 
-3000 




-500 




-500 








-100 




3 
•3 


■A 


■5 




5 
■6 








-4000 
-5000 




-1000 








-500 




-200 




? 




■4 


■5 






•20 




-6000 




-2000 












-300 




1-2 


3 






5 




























.] 








■5 






>- 


- 








MOOO 








-400 


O 


\° 






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30 


< 

<r 


-7000 




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•1100 




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z 




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O 




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t 

z 




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N 




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N 




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uu 




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a 


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I 
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z 




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z 


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# EQUIVALENT TO LOCAL STANDARD TIME ± FIFTEEN MINUTES 

t ON RAINY DAYS VALUES WILL BE ABOUT HALF THOSE SHOWN 

* APPROXIMATELY EQUIVALENT TO AVERAGE SKY BRIGHTNESS IN FOOTLAMBERTS 

FIG. 9-1. Average daylight illumination at various times and in various planes at 
42 degrees north latitude. 1 



DAYLIGHTING 



9-3 



Glass and efficiency 

TYPE 

Clear sheet 

Ribbed 

Rough or hammered 

For the average office win- 
dow with clear water-white 
glass, a single transom, and 
few mullions, 80 per cent is a 
representative efficienc} 7 . A 
factor of 60 per cent should 
be used for the average fac- 
tory window with many small 
panes. 

Maintenance factors. Main- 
tenance factors will vary over 
a wide range depending on the 
local atmosphere, the cleaning 
schedule, the glass surface and 
the window slope. Values for 
factory windows cleaned twice 
each year are given in Fig. 9-2. 



Three types of window glass are in common use: 

CLEAN TRANSMITTAL CE 

82-90% (depending on color) 

67-84% (depending on color and pattern) 

50-8S% (depending on color and pattern) 




O 10 20 30 40 50 60 70 80 
ANGLE FROM VERTICAL IN DEGREES 

FIG. 9-2. The effect of slope on the dirt col- 
lection rate of a typical factory window is re- 
vealed by this plot of the maintenance factor 
(glass transmittance six months after cleaning) 
as a function of slope. 2 



Window Design Evaluation and Comparison 

Tables 9-1, 9-2, and 9-3* and Figs. 9-3 to 9-6, inclusive, which were 
developed from test data on factory -type windows, facilitate comparisons 
between different designs. 2 The values given are based on a sky brightness 
of approximately 980 footlamberts and a series of windows 100 feet long. 
The possible contribution of interreflections is not included. 



SKY BRIGHTNESS: 
9B0 FOOTLAMBERTS 
CLEAN WINDOW — 
IV TRANSM ITTANCE :0.64| 
MAINTENANCE 
FACTOR : 0.5 . 




40 



5 10 15 20 25 

DISTANCE FROM WINDOW 

IN FEET 

FIG. 9-3. Effect of window 
height on daylight illumina- 
tion on a horizontal plane at 
sill height in a building with 
a 100-foot-long series of win- 
dows in one wall (neglecting 
interreflections). 2 



5 10 
p 





SKY BRIGHTNESS - . 980 FOOTLAMBERTS 
CLEAN WINDOW TRANSMITTANCE : 0.64 




\ 


V MAINTENANCE FACTOR - . 0.5 J 


1 




\ \ 
\ 














/ 






leftVJ 


^LEFT AND RIGHT/ 


''right 








— 1 


V 


■^ 




„/ 









10 15 20 25 20 15 10 5 
DISTANCE FROM WALLS IN FEET 



FIG. 9-4. Daylight illumination at various 
points on a horizontal plane at sill height in a 
50-foot-wide rectangular building with a 100- 
foot-long series of windows (8 feet 6f inches 
high) in each of two opposing walls (neglecting 
interreflections) .- 



• Pages 9-7, 9-8, aad 9-9 



9-4 I E S LIGHTING HANDBOOK 

The measured values have been multiplied by an efficiency factor of 64 
per cent (80 per cent glass transmittance times 80 per cent absorptance for 
transoms, muntins, and mullions) and by a maintenance factor (50 per 
cent for vertical windows or 25 per cent for windows with a 30-degree 
slope). 

Figure 9-7* gives factors by which the tabulated and plotted values may 
be multiplied in order to obtain values for other than 100-foot window 
lengths. To determine illumination for values of sky brightness other 
than 980 footlamberts, the data should be divided by 980 and multiplied 
by the new brightness. 

The following rules of thumb direct attention to several variables which 
should be considered when different designs are being evaluated 

1 . The window area should be as large as practicable and at least equal 
to 25 per cent of the floor area. When near-by trees or buildings reduce the 
sky area visible from the windows, the ratio of window to floor area should 
be increased above 25 per cent. 

2. Windows should be placed as high in a wall as practicable and in more 
than one wall whenever possible. 

3. Transoms, muntins, and mullions should be made as small in cross 
section as possible and a minimum number should be used. 

4. Deep reveals should be splaj'ed. 

5. For a given window area, small in comparison to that of a wall, greater 
uniformity of illumination will result from two small windows spaced not 
farther apart than their combined width than from a single centered 
window. 

6. Some type of brightness control should be planned for windows which 
will receive direct sunlight. 

Brightness Control 

In offices, roller shades or Venetian blinds are used to reduce the apparent 
source brightness. In factories, saw-tooth roofs usually face north and 
are sloped so that no direct sunlight is admitted. A saw-tooth roof can 
be constructed with windows facing south; however, with this orientation 
some means for diffusing the direct sunlight should be used in summer. 
Diff users reduce the maximum illumination to a greater extent than they 
do the minimum and therefore improve uniformity. 

A coat of whitewash or other diffuse transmittance material sometimes 
is sprayed on a glass window late in the spring and washed off in the fall. 
It should be noted that ordinary whitewash (slaked lime) may etch a glass 
surface slightly during the summer and consequently hasten the accumula- 
tion of dirt the following winter. 

Heat-absorbing glass with permanent diffusing surfaces has lower trans- 
mittance than ordinary glass, but when it is used the application and 
removal of the diff user are unnecessary. 

Painting. Finishing an interior with high-reflectance paint or other 
coating increases the daylight as well as the electrical illumination level 

• Page 9-7. 



DAYLIGHTING 



9-5 




30~SLOF€ 

eo" slope 12 FT 



over that which might be expected with low -reflectance surfaces. The 
amount of increase depends upon window area, room dimensions, wall and 
ceiling reflectances, and ground brightness. To coat the exterior of the 
saw-tooth roof and vertical walls of courts or of adjacent buildings with a 
high-reflectance material will increase the daylight illumination also. 

Roof Windows 

A building can be too wide to 
obtain adequate daylight illumi- 
nation through side-wall windows 
alone. Roof windows may be 
used to increase the daylight il- 
lumination in the center of the 
structure. Roof windows are of 
three general types: (1) vertical 
or sloping in monitors; (2) verti- 
cal or sloping in saw teeth; (3) 
skylights. 

Figure 9-5 represents a building 
100 feet wide with windows in the 
side walls 12 feet high. On the 
roof of this building are shown: 
(1) a monitor with 6-foot vertical 
windows; (2) a monitor with 6- 
foot windows on a 30-degree 
slope; (3) 6-foot skylights on a 
60-degree slope. 

Notice that the glass area is the 
same in all three, and that each 



45 

(3 40 

_l 

a 

^ 35 

f? 30 



Z 25 
O 



\ SKY BRIGHTNESS: 980 FOOTLAM&ZRTS / 

_1 CLEAN WINDOW TRANCE ITTANCE: 0.64 L_ 

\ MAINTENANCE FACTOR : 05(VERTICAL)( 

\ 0.25 (30*SLOPE) 0.13(80° SLOPE) I 


J 
























VERTICAL 
i 
















r 


1— ■ N^, 


.— 30° 
SLOPE 














P 




\ / 




Vf 








^60° SLOPE 

1 i 









10 

10 20 30 40 50 40 30 20 10 
DISTANCE FROM WALLS IN FEET 

FIG. 9-5. Effect of monitor design on 
daylight illumination at various points on 
a horizontal plane at sill height, in a 100- 
foot-wide rectangular building with a 100- 
footdong series of windows (12 feet high) 
in each of two opposing walls (neglecting 
interreflections) ."■ 



glass area is so located as to provide the best daylight illumination of which 
it is capable. The curves show the footcandles transmitted to the hori- 
zontal reference plane by each of these three roof designs added to those 
transmitted by the side-wall windows. 

Monitor design. As a general rule, the best daylighting can be secured 
through vertical windows in a monitor half as wide as the building. A 
monitor should be no higher than half its width, and should be at least 
twice as wide as its window height. When the width of a monitor is less 
than twice the height of its windows, light transmitted by the upper panes 
will be cut off by the roof line. 

Increasing the height of a monitor, whether it be wide or narrow, in- 
creases the minimum illumination faster than it does the maximum and thus 
helps to secure uniformity. Occasionally, sloping glass in a wide monitor 
results in a greater proportionate increase in the minimum illumination 
level in a building than in the maximum. Whether the windows are 
vertical or sloping, an increase in their glass area always results in an in- 
crease in the minimum illumination. 



9-6 



I E S LIGHTING HANDBOOK 



Saw-tooth roofs. Saw-tooth roofs often are provided in a building so 
wide that light from side-wall windows is ineffective over a large area in 
the center of the building. Frequently they are used to provide a uniform 
level of north-sky light. 

Usually the faces of the teeth (the sides containing windows) are turned 
to the north to secure the advantages of daylight with a minimum discom- 
fort from direct sunlight. In some instances it may be advantageous to 
face the saw teeth to the south. The southern sky usually is brighter than 
the northern sky and thus ensures maximum daylight illumination in the 
dark winter months. For southern orientations, probably it will be neces- 
sary to provide some means of brightness control for summer use. 

The design and location of saw teeth should follow the principles out- 
lined for monitors. Usually the open width (base of triangle) should not 
be less than twice the height of saw-tooth windows. 

Thirty -degree sloping windows six months after cleaning will admit no 
more light than vertical windows six months after cleaning. Either is 
likely to provide more than 10 footcandles on the horizontal reference plane 
if the glass area is more than 30 per cent of the floor area. Narrowing the 

span of the saw teeth or increasing 
the height of the windows increases 
the minimum daylight illumination 
faster than it increases the maximum. 
This is illustrated in the diagrams of 
Fig. 9-6. The illumination curve for 
a 40-foot saw tooth is shown at the 
left. At the right is shown what 
happens when the 40-foot saw tooth 
is converted into two 20-foot was 
teeth, the window height remaining 

t^t/-. r, n t^cc r xi r unchanged. Note how the minimum 

1IG. 9-6. Effect of saw-tooth root ...... , ., , 

design on relative daylight illumination lamination increases while the mal- 
distribution inside a building (neglect- mum illumination remains about the 
inginterreflections). same, thus improving the uniformity. 



■« 40 FT »» 



-20FT-" 



MAXIMUM^ 




Multistory Buildings 

Multistory buildings frequently are erected in congested districts. They 
often are built in the form of an E or a U . The chief multistory daylighting 
problem is the interference caused by surrounding buildings or by other 
parts of the same building. 

When the windows in a multistory building are of uniform height and 
any structure is located near enough to shade them, the illumination on any 
given floor of the building will be considerably lower than it is on the floor 
above. 



DAYLIGHTING 



9 7 



window length: 
200 ft or more 




20 30 40 50 60 70 80 90 100 110 120 
DISTANCE IN FEET FROM PLANE OF WINDOW 



130 140 



FIG. 9-7. To determine the daylight illumination at any distance from a window- 
series of a length other than 100 feet, multiply the value for a lOO-foot-long series 
(found in Figs 9-3, 9-4, & 9-5), by the appropriate factor selected from these curves. 2 

Table 9-1. Daylight Illumination (in Footcandles) Provided at Various 

Points on a Horizontal Plane at Sill Height by a 100-Foot-Long 

Series of Sidewall Windows of Various Heights* 



FEET 
BACK 












WINDOW HEIGHT 












FROM 




























WINDOW 


S'2* 


6'10" 
30 


8'6" 


10'3' 


ii'ii" 


13'7" 


15'4" 


17'0" 


18'9* 


20 '5' 


22'2" 


23'n* 


25'7' 


5 


25 


35 


39 


42 


44 


47 


48 


50 


52 


53 


54 


55 


10 


13 


16 


20 


24 


28 


32 


35 


38 


40 


42 


44 


45 


47 


15 


7.5 


9.8 


12 


16 


19 


22 


24 


27 


30 


33 


34 


36 


38 


20 


4.8 


6.2 


8 


10 


13 


16 


18 


21 


23 


26 


28 


30 


32 


25 


3.3 


4.3 


5.5 


7.3 


9.6 


12 


14 


16 


18 


21 


22 


24 


26 


30 


2.4 


3.2 


4.1 


5.5 


7.3 


8.8 


11 


12 


14 


17 


18 


20 


21 


35 


1.8 


2.4 


3.2 


4.2 


5.5 


6.8 


8.1 


10 


12 


13 


15 


16 


18 


40 


1.4 


1.8 


2.4 


3.3 


4.4 


5.5 


6.5 


7.8 


9.2 


11 


12 


13 


15 


45 


1.1 


1.5 


2.0 


2.6 


3.5 


4.3 


5.2 


6.4 


7.4 


8.6 


9.6 


11 


12 


50 


0.9 


1.2 


1.6 


2.1 


2.8 


3.4 


4.2 


5.0 


6.0 


7.0 


8.0 


9 


10 


55 


0.7 


1.0 


1.3 


1.8 


2.3 


2.8 


3.5 


4.2 


4.9 


5.8 


6.6 


7.5 


8.5 


60 


0.6 


0.8 


1.1 


1.4 


1.9 


2.3 


2.9 


3.4 


4.1 


4.8 


5.6 


6.4 


7.2 


65 


0.5 


0.7 


0.9 


1.2 


1.6 


2.0 


2.4 


2.9 


3.4 


4.0 


4.6 


5.3 


6.1 


70 


0.4 


0.6 


0.8 


1.0 


1.4 


1.7 


2.1 


2.5 


3.0 


3.5 


4.0 


4.6 


5.1 


75 


0.4 


0.5 


0.7 


0.9 


1.2 


1.5 


1.8 


2.2 


2.5 


3.0 


3.5 


4.0 


4.6 


80 


0.3 


0.4 


0.6 


0.8 


1.0 


1.3 


1.6 


1.9 


2.2 


2.6 


3.1 


3.5 


4.0 


85 


0.3 


0.4 


0.5 


0.7 


0.9 


1.1 


1.4 


1.7 


2.0 


2.3 


2.6 


3.1 


3.5 


90 


0.2 


0.3 


0.5 


0.6 


0.8 


1.0 


1.2 


1.5 


1.8 


2.1 


2.4 


2.8 


3.1 


95 


0.2 


0.3 


0.4 


0.5 


0.7 


0.9 


1.1 


1.3 


1.5 


1.8 


2.1 


2.5 


2.8 


100 


0.2 


0.3 


0.4 


0.5 


0.7 


O.S 


1.0 


1.2 


1.4 


1.7 


1.9 


2.2 


2.5 


105 


0.2 


0.3 


0.3 


0.4 


0.6 


0.7 


0.9 


1.1 


1.3 


1.5 


1.8 


2.0 


2.3 


110 


0.2 


0.2 


0.3 


0.4 


0.6 


0.7 


0.8 


1.0 


1.1 


1.4 


1.6 


1.9 


2.1 


115 


0.2 


0.2 


0.3 


0.4 


0.5 


0.6 


0.7 


0.8 


1.0 


1.3 


1.5 


1.7 


1.9 


120 


0.1 


0.2 


0.3 


0.4 


0.5 


0.5 


0.7 


0.8 


0.9 


1.2 


1.3 


1.6 


1.7 


125 


0.1 


0.2 


0.2 


0.3 


0.5 


0.5 


0.7 


0.7 


0.9 


1.1 


1.2 


1.4 


1.6 


130 


0.1 


0.2 


0.2 


3 


0.4 


0.5 


0.6 


0.7 


0.8 


1.0 


1.1 


1.3 


1.5 


135 


0.1 


0.2 


0.2 


0.3 


0.4 


0.5 


0.6 


0.7 


0.8 


1.0 


1.0 


1.2 


1.3 


140 


0.1 


0.1 


0.2 


0.3 


0.4 


0.5 


0.6 


0.7 


0.8 


0.9 


1.0 


1.1 


1.2 



•Sky brightness, 980 footlamberts; efficiency factor, 0.64; maintenance factor, 0.50; interreflcctions 
neglected.' Correction factors for other lengths given in Fig. 9-7. 



9-8 



I E S LIGHTING HANDBOOK 



The daylighting on every floor of a multistory building can be improved 
by widening the distance between it and the shading structure. The 
daylighting on the lower floors will be improved more than that on the 
upper floors. Closing the open space of an E- or a U-shaped building to 
form a court reduces the illumination within the building; the greatest 
reduction occurs on the lower floors. 

Service towers on the near walls of adjacent buildings tend to reduce 
the minimum illumination on lower floors of the opposite buildings as 
much as one third to one half. 



Table 9-2. Daylight Illumination (in Footcandles) Provided at Various 

Points on a Horizontal Plane by a 100-Foot-Long Series of 

Sidewall Windows of Various Heights with Sills at 

Various Heights Above the Plane* 





SILL HEIGHT ABOVE HORIZONTAL REFERENCE PLANE 


FEET 
BACK 




IS feet 


25 feet 


35 feet 


45 feet 


FROM 
WIN- 
DOW 
















Window 


ieight 




Window height 


Window height 


Window height 




>0 r-i 


o 
o 


o 


o 


o 


s 


O 


oo 


rp 


o 


s 


O 

o 


o 


© 


o 


C-4 


O 


£ 


O 


5 


3.04.0 


5.1 


6.0 


6.7 


1.2 


1.5 


1.8 


2.1 


2.5 


0.6 


0.9 


1.1 


1.4 


1.6 


0.4 


0.9 


1.4 


2.0 


2.9 


10 


5.817.4 


9.8 


11.2 


12.0 


2.2 


3.0 


3.6 


4.3 


4.7 


1.3 


1.9 


2.3 


2.9 


3.6 


1.2 


1.7 


2.4 


3.3 


4.2 


15 


6.68.0 


10.6 


12.8 


13.8 


3.0 


4.4 


5.2 


6.5 


7.1 


1.9 


2.7 


3.3 


4.3 


5.2 


1.7 


2.5 


3.3 


4.1 


5.1 


20 


6.0 


7.7 


9.8 


12.1 


13.6 


3.5 


5.1 


6.3 


7.8 


9.0 


2.4 


3.3 


4.0 


5.4 


6.6 


2.3 


3.2 


4.0 


4.8 


5.8 


25 


5.1 


6.8 


8.5 


10.6 


12.1 


3.8 


5.2 


6.6 


S.3 


9.8 


2.7 


3.6 


4.5 


5.9 


7.3 


2.7 


3.S 


4.6 


5.4 


6.3 


30 


4.3 


5.8 


7.5 


9.2 


10.7 


3.6 


5.0 


6.1 


8.4 


10.0 


2.9 


3.7 


4.6 


6.0 


7.5 


2.9 


4.2 


4.9 


5.8 


6.6 


35 


3.6 


4.8 


6.4 


7.8 


9.1 


3.4 


4.6 


6.2 


7.8 


9.2 


2.7 


3.6 


4.5 


5.9 


7.5 


2.8 


4.0 


4.9 


5.7 


6.4 


40 


3.1 


4.0 


5.4 


6.0 


7.8 


3.1 


4.2 


5.5 


7.0 


8.1 


2.5 


3.4 


4.3 


5.8 


7.1 


2.6 


3.7 


4.6 


5.5 


6.2 


45 


2.5 


3.4 


4.5 


5.5 


6.6 


2.8 


3.7 


4.9 


6.2 


7.3 


2.3 


3.1 


4.0 


5.3 


6.8 


2.4 


3.5 


4.4 


5.2 


5.9 


50 


2.1 


2.8 


3.7 


4.7 


5.6 


2.6 


3.3 


4.4 


5.5 


6.5 


2.1 


2.8 


3.7 


4.9 


6.4 


2.2 


3.2 


4.0 


4.9 


5.5 


55 


1.7 


2.4 


3.0 


3.9 


4.8 


2.3 


2.9 


3.9 


4.9 


5.8 


1.9 


2.6 


3.3 


4.5 


5.9 


2.0 


2.9 


3.7 


4.5 


5.3 


60 


1.3 


2.0 


2.5 


3.3 


4.0 


2.0 


2.6 


3.4 


4.4 


5.2 


1.7 


2.3 


3.0 


4.1 


5.4 


1.9 


2.6 


3.5 


4.2 


4.9 


65 


1.1 


1.7 


2.1 


2.8 


3.4 


1.8 


2.3 


3.1 


3.9 


4.6 


1.6 


2.1 


2.7 


3.7 


4.8 


1.7 


2.4 


3.2 


3.9 


4.6 


70 


0.9 


1.4 


1.8 


2.4 


3.0 


1.5 


2.1 


2.7 


3.4 


4.0 


1.4 


1.9 


2.4 


3.4 


4.3 


1.5 


2.2 


2.9 


3.6 


4.3 


75 


0.8 


1.2 


1.5 


2.1 


2.5 


1.4 


1.9 


2.4 


3.0 


3.5 


1.3 


1.8 


2.2 


3.0 


3.9 


1.4 


2.0 


2.7 


3.4 


4.1 


80 


0.611.0 


1.3 


1.8 


2.2 


1.3 


1.6 


2.2 


2.7 


3.1 


1.2 


1.6 


2.0 


2.7 


3.5 


1.2 


1.8 


2.4 


3.1 


3.8 


85 


0.50.9 


1.2 


1.6 


2.0 


1.1 


1.5 


1.9 


2.4 


2.8 


1.1 


1.4 


1.8 


2.4 


3.1 


1.1 


1.7 


2.2 


2.9 


3.6 


90 


0.50.8 


1.0 


1.4 


1.8 


0.9 


1.3 


1.7 


2.1 


2.5 


1.0 


1.3 


1.7 


2.2 


2.8 


1.0 


1.5 


2.1 


2.7 


3.3 


95 


0.4 ! 0.6 


0.9 


1.2 


1.6 


0.8 


1.1 


1.5 


1.8 


2.2 


0.9 


1.2 


1.5 


2.0 


2.5 


1.0 


1.4 


2.0 


2.5 


3.1 


100 


0.40.6 


0.8 


1.1 


1.4 


0.7 


0.9 


1.2 


1.5 


2.0 


0.9 


1. 1 


1.4 


1.8 


2.3 


0.9 


1.3 


1.9 


2.3 


2.9 


105 


0.40.5 


0.7 


0.9 


1.3 


0.5 


0.8 


1.0 


1.4 


1.8 


0.8 


1.1 


1.3 


1.7 


2.1 


I) S 


1.2 


1.7 


2.2 


2.7 


110 


0.3,0.5 


0.6 


0.8 


1.1 


0.4 


0.6 


0.9 


1.2 


1.2 


0.8 


1.0 


1.2 


1.6 


2.0 


O.S 


1.1 


1.6 


2.1 


3.0 


115 


0.3,0.4 


0.5 


0.7 


1.0 


0.4 


0.5 


0.7 


1.0 


1.4 


0.7 


1.0 


1.2 


1.5 


1.9 


0.7 


1.0 


1.5 


2.0 


2.3 


120 


0.30.4 


0.5 


0.6 


0.8 


0.3 


0.5 


0.6 


0.9 


1.2 


0.7 


0.9 


1.1 


1.4 


1.7 


0.7 


1.0 


1.4 


1.8 


2.2 


125 


0.20.3 


0.4 


0.6 


0.8 


0.3 


0.4 


0.6 


0.8 


1.1 


0.7 


0.9 


1.1 


1.3 


1.6 


0.6 


0.9 


1.3 


1.7 


2.1 


130 


0.20.3 


0.4 


0.5 


0.7 


0.2 


0.4 


0.5 


0.7 


1.0 


0.6 


0.9 


1.1 


1.3 


1.5 


0.6 


0.9 


1.2 


1.6 


1.9 


135 


0.2 ! 0.3 


0.4 


0.5 


0.6 


0.2 


0.3 


0.4 


0.6 


0.9 


(i li 


0.8 


1.0 


1.2 


1.4 


0.6 


O.S 


1.1 


1.5 


1.9 


140 


0.2,0.3 

i 


0.3 


0.4 


0.6 


0.2 


0.3 


(i i 


0.5 


0.8 


0.6 


O.S 


1.0 


1.2 


1.4 


0.6 


0.8 


1.1 


1.5 


1.8 



* Sky brightness, 980 footlamberts; efficiency factor, 0.64; maintenance factor, 0.50; interreflections 
neglected. 2 Correction factors for other lengths given in Fig. 9-7. 



DAYLIGHTING 



9-9 



Where uniformity throughout a building is important, approximately equal 
minimum daylight can be obtained on all floors by increasing (below the 
top floor) the window heights and window-to-floor area ratios. The great- 
est increase is necessary on the ground floor. The top-story window area 
should equal about 30 per cent of the floor area. 

The use of high-reflectance brick, tile, or paint for the walls of enclosed 
courts in place of low-reflectance surfaces may produce a large increase in 
daylight illumination on the lower floors. 



Table 9-3. Daylight Illumination (in Footcandles) Provided at Various 

Points on a Horizontal Plane by a 100 -Foot-Long Series of 

30-Degree Sloping Windows of Various Heights with 

Sills at Various Heights above the Plane* 





SLANT HEIGHT OF SILLJ 


FEET 
























FROM 
PLANE 




15 Feet 




25 Feet 




35 Feet 




45 Feet 


OF 
WINDOWt 




slant Height 
of Window 




Slant Heigh 
of Window 




Slant 
ofWi 


Height 
ndow 




Slant Height 
of Window 




3'0' 

1.6 


6'0" 

2.6 


9'0' 

3.3 


12'0" 
3.9 


3'0" 

0.6 


6'0' 
1.0 


9'0" 

1.5 


12'0" 

2.1 


3'0' 

0.5 


6'0" 

0.8 


9'0" 
1.1 


12 '0" 

1.5 


3'0" 

0.2 


6'0* 

0.4 


9'0' 

0.6 


12'0" 


5 


0.8 


10 


4.8 


8.3 


10.6 


16.9 


1.6 


2.3 


3.5 


4.6 


0.9 


1.5 


2.2 


2.9 


0.5 


0.8 


1.3 


1.8 


15 


7.0 


13.8 


18.4 


21.3 


2.5 


4.1 


6.3 


7.4 


1.3 


2.3 


3.4 


4.5 


0.8 


1.6 


2.3 


2.9 


20 


4.9 


10.1 


16.3 


19.3 


3.3 


6.2 


8.9 


10.1 


1.7 


3.1 


4.6 


6.0 


1.2 


2.4 


3.3 


4.3 


25 


3.5 


6.8 


11.9 


16.2 


3.9 


7.1 


9.6 


11.6 


2.0 


3.8 


5.7 


7.5 


1.6 


3.1 


4.5 


5.S 


30 


2.5 


4.9 


8.5 


12.8 


3.5 


6.8 


9.5 


11.9 


2.4 


4.6 


6.7 


8.9 


1.5 


3.9 


5.8 


7.4 


35 


1.8 


3.8 


6.3 


9.8 


3.0 


6.1 


8.9 


11.7 


2.8 


5.3 


7.6 


10.0 


2.3 


4.5 


6.8 


8.6 


40 


1.3 


3.0 


5.1 


7.8 


2.6 


5.4 


8.1 


11.1 


2.9 


5.6 


8.1 


10.6 


2.5 


4.7 


7.1 


9.1 


45 


1.0 


2.4 


4.3 


6.2 


2.2 


4.7 


7.2 


9.8 


2.7 


5.2 


7.6 


10.0 


2.4 


4.7 


7.0 


9.1 


50 


0.8 


1.9 


3.6 


5.3 


1.9 


4.0 


6.3 


8.6 


2.3 


4.6 


6.9 


9.1 


2.3 


4.5 


6.9 


8.9 


55 


0.6 


1.6 


3.0 


4.4 


1.7 


3.5 


5.3 


7.5 


2.0 


4.1 


6.2 


8.3 


2.1 


4.2 


6.5 


8.6 


60 


0.5 


1.4 


2.5 


3.8 


1.4 


3.0 


4.5 


6.4 


1.7 


3.6 


5.5 


7.5 


1.9 


3.9 


6.0 


8.0 


65 


0.5 


1.2 


2.1 


3.2 


1.2 


2.5 


3.8 


5.5 


1.5 


3.1 


4.9 


6.8 


1.8 


3.5 


5.5 


7.3 


70 


0.4 


1.0 


1.7 


2.7 


1.0 


2.1 


3.2 


4.7 


1.3 


2.6 


4.3 


6.1 


1.6 


3.2 


5.0 


6.7 


75 


0.4 


0.8 


1.5 


2.3 


0.9 


1.7 


2.7 


4.0 


1.1 


2.3 


3.8 


5.4 


1.4 


2.9 


4.5 


6.1 


80 


0.3 


0.7 


1.2 


1.9 


0.7 


1.4 


2.2 


3.3 


0.9 


2.0 


3.2 


4.8 


1.3 


2.6 


4.0 


5.5 


85 


0.3 


0.6 


1.0 


1.6 


0.6 


1.2 


1.9 


2.7 


0.8 


1.7 


2.8 


4.1 


1.1 


2.3 


3.5 


5.0 


90 


0.3 


0.5 


0.9 


1.4 


0.5 


1.0 


1.6 


2.3 


0.7 


1.5 


2.4 


3.5 


1.0 


2.0 


3.1 


4.4 


95 


0.3 


0.4 


0.7 


1.1 


0.4 


0.9 


1.3 


1.9 


0.6 


1.3 


2.1 


3.0 


0.9 


1.8 


2.8 


3.9 


100 


0.2 


0.4 


0.6 


1.0 


0.4 


0.7 


1.2 


1.6 


0.5 


1.1 


1.9 


2.6 


0.8 


1.6 


2.5 
2.3 


3.5 


105 


0.2 


0.3 


0.5 


0.8 


0.3 


0.6 


1.0 


1.5 


0.5 


1.0 


1.6 


2.3 


0.7 


1.4 


3.2 


110 


0.2 


0.3 


0.5 


0.7 


0.3 


0.6 


0.9 


1.3 


0.4 


0.9 


1.4 


2.0 


0.6 


1.3 


2.1 


2.9 


115 


0.2 


0.3 


0.4 


0.6 


0.3 


0.5 


0.8 


1.1 


0.4 


0.8 


1.3 


1.8 


0.6 


1.2 


1.9 


2.6 


120 


0.2 


0.3 


0.4 


0.5 


0.2 


0.5 


0.7 


1.0 


0.4 


0.7 


1.1 


1.6 


0.5 


1.1 


1.8 


2.4 


125 


0.2 


0.2 


0.4 


0.5 


0.2 


0.4 


0.6 


0.9 


0.3 


0.7 


1.0 


1.4 


0.5 


1.0 


1.6 


2.2 


130 


0.2 


0.2 


0.3 


0.4 


0.2 


0.4 


0.6 


0.8 


0.3 


0.6 


0.9 


1.3 


0.4 


0.9 


1.4 


2.0 


135 


0.2 


0.2 


0.3 


0.4 


0.2 


0.4 


0.5 


0.8 


0.2 


0.6 


0.9 


1.2 


0.4 


0.9 


1.3 


1.8 


140 


0.1 


0.2 


0.3 


0.4 


0.2 


0.4 


0.5 


0.7 


0.2 


0.5 


0.8 


1.1 


0.3 


0.8 


1.2 


1.6 



* Sky brightness, 980 footlarnberts; efficiency factor, 0.64; maintenance factor, 0.50; interreflections 
neglected. 2 Correction factors for other lengths given in Fig. 9-7. 

t Measured from intersection of window plane and horizontal reference plane. 

t Measured between sill and intersection of window plane and horizontal reference plane. 



f 



9-10 



I E S LIGHTING HANDBOOK 



REFERENCES 



1. Kimball, H. H., "Daylight Illumination on Horizontal, Vertical and Sloping Surfaces," Trans. Ilium. 

Eng.Soc, May, 1923. -"Sky Brightness and Daylight Illumination Measurements," Trans. Ilium. Eng. 

Soc. , October, 1921. 

2. Randall, W. C, and Martin, A. J., "Predetermination of Davlighting by the Fenestra Method " Trans 
Ilium. Eng. Soc, March, 1930. 

3. Brown, L. H., "Control of Natural Light in Schoolrooms," Trans. Ilium. Eng. Soc, March 1940- June 
1939. 

4. Biesele, It. L., Jr., Folsom, W. E., and Graham, V. J., "Control of Natural Light in Classrooms," Ilium. 
Eng., September, 1945. 

5. Harmon, D B., "The Rosedale School, A Demonstration in Classroom Lighting, Decoration and Seat- 
ing," Texas State Board of Health, Austin, Texas, 1947 

See also 

6. Baker, II. J., "Daylight Recording at the Edison Electric Illuminating Co. of Boston," Trans. Ilium. 
Eng. Soc, May, 1925. 

7. Beal, A. F., "Some Factors Affecting Daylight Lighting of Interiors," Trans. Ilium. Eng. Soc, March, 
1927. 

8. Brown, W. S., "Practical Daylight Calculations for Vertical Windows," Trans. Ilium. Eng. Soc, March, 
1926. 

9. Bull, H. S., "A Nomogram to Facilitate Daylight Calculations," Trans. Ilium. Eng. Soc, May, 1928. 

10. Coblentz, W. \V., "The Biologically Active Component of Ultraviolet in Sunlight and Daylight," 

Trans. Ilium. Eng. Soc, July, 1931. ."Spectral Characteristics of Light Sources and Window Materials 

Used in Therapy," Trans. Ilium. Eng. Soc, March, 1928. 

11 . Coblentz, W. W., and Stair, R., "The Effect of Solarization upon the Ultraviolet Transmission of Win- 
dow Materials," Trans. Ilium. Eng. Soc, November, 1928. 

12. Committee on Natural Lighting of the I.E.S., "A Bibliography of Natural Lighting," Trans. Ilium. 
Eng. Soc, March, 1929. 

13. Elvegard, E., and Sjostedt, G., "The Calculation of Illumination from Sun and Sky," Trans. Ilium. 
Eng. Soc, April, 1940. 

14. Estey, R. S, and Miller, R. A., "The Transmission of Solar Radiation through Heat-Absorbing Glass, 
Trans. Ilium. Eng. Soc, May, 1935. 

15. Gage, H. P., "Hygienic Effects of Ultraviolet Radiation in Daylight," Trans. Ilium. Eng. Soc, April, 
1930. 

16. Gamble, D. L., "The Influence of the Reflecting Characteristics of Wall Paints upon the Intensity and 
Distribution of Artificial and Natural Illumination," Trans. Ilium. Eng. Soc, April, 1933. 

17. Greene, B. F., "Natural Light Reflected from the Ceiling," Ilium. Eng., June, 1946. 

18. Greider, C. E., and Downes, A. C, "Sunlight — Natural and Synthetic," Trans. Ilium. Eng. Soc, 
April, 1930. 

19. Harmon, D. B., "Lighting and Child Development," Ilium. Eng. , April, 1945. 

20. Higbie, H. H., "Treating the Windows to Conserve Daylight," Trans. Ilium. Eng. Soc, March, 1929 

— ■ ."Control of Illumination from Windows," Trans. Ilium. Eng. Soc, March, 1927. ."Prediction ol 

Daylight from Vertical Windows, "Trans. Ilium. Eng. Soc, May, 1925. 

21. Higbie, II. H., and Levin, A., "Further Experimental Data on the Prediction of Daylight from Win- 
dows," Trans. Ilium. Eng. Soc, April, 1926. ."Prediction of Daylight from Sloping Windows," Trans. 

Ilium. Eng. Soc, March, 1926. 

22. Higbie, H. H., and Bull, II. S., "How Glass Affects Your Davlighting," Trans. Ilium. Eng. Soc, March, 
1931. 

23. Higbie, H. H., and Turner-Szymanowski, W., "Calculation of Daylighting and Indirect Artificial 
Lighting by Protractor Method," Trans. Ilium. Eng. Soc, March, 1930. 

24. Hobbie, E. H., and Little, W. F., "Transmission of Light through Window Glass," Trans. Ilium. Eng. 
Soc, March, 1927. 

25. Ives, J. E., "Records of Daylight by the Photoelectric Cell," Trans. Ilium. Eng. Soc, May, 1925. 

26. Ives, J. E., and Knowles, F. L., "Recent Measurements of the Brightness of the Clear North Sky in 
Washington, D. C," Trans. Ilium. Eng. Soc, March, 1935. 

27. Johnston, H. L., "Daylight Variations," Trans. Ilium. Eng. Soc, March, 1940; July, 1939. 

28. Kimball, H. H., "Records of Total Solar Radiation Intensity and Their Relation to Daylight Inten- 
sity," Trans. Ilium. Eng. Soc, May, 1925. 

29. Knowles, F. L.,and Ives, J. E., "Sill Ratio Method of Measuring Daylight in the Interior of Buildings,' 
Trans. Ilium. Eng. Soc, May, 1939. 

30. Kunerth, W., and Miller, R. D., "Variations of Intensities of the Visible and of the Ultraviolet in Sun- 
light and in Skylight," ?Ya»s. Ilium. Eng. Soc, January, 1932. 

31. Logan, II. L., "Specification Points of Brightness," Trans. Ilium. Eng. Soc, September, 1939. 

32. Luckiesh, M., "Simulating Sunlight," Trans. Ilium. Eng. Soc, April, 1930. 

33. Meller, H. B., Hibben, S. G., and Warga, M. E., "Studies of Ultraviolet in Daylight," Trans. Ilium. 
Eng. Soc, January, 1932. 

34. Moon, P., and Spencer, D. E., "Light Distribution from Rectangular Sources," J. Franklin Inst., 
March, 1946. — /'Illumination from a Non-uniform Sky," Ilium. Eng., December, 1942. 

35. Nickerson, D., "Artificial Daylighting Studies," Trans. Ilium. Eng. Soc, December, 1939. 

36. Prideaux, G. F., "An Artificial Sunshine Solarium," Ilium. Eng., November, 1946. 

37. Randall, W. C, "Designing for Daylight," Trans. Ilium. Eng. Soc, July, 1927. ■ — , "Saw-tooth De- 
sign — Its Effect on Natural Illumination," Trans. Ilium. Eng. Soc, March, 1926. 

3S. Randall, W. C, and Martin, A. J., "The Window as a Source of Light," Trans. Ilium. Eng. Soc, March, 

1932. ."Daylighting in the Home," Trans. Ilium. Eng. Soc, March, 1931. ,"The Utilization 6f 

Exterior Reflecting Surfaces in Daylighting," Trans. Ilium. Eng. Soc, March, 1929. — ."Making Your 

Windows Deliver Daylight," Trans. Ilium. Eng. Soc, March, 1927. 

39. Reid, K. M., and Chanon, II. J., "Daytime Lighting Requirements for Tunnel Entrances," Ilium. 
Eng., March, 1940. 

40. Taylor, A. H., "The Color of Daylight," Trans. Ilium. Eng. Soc, February, 1930. 

41. Thomas, G. W., "The Status of Natural Lighting in Modern Building Codes," Trans. Ilium. Eng. Soc, 
March, 1932. 

42. Vogel, A., Randall, W. C, Martin, A. J., and Benford, F., "Daylighting in Multi-Story Industrial 
Buildings," Trans. Ilium. Eng. Soc, February, 1928. 

43. Wynkoop, F., "Advances in the Art of School-room Daylighting," Architectural Record, July, 1945. 



< 



SECTION 10 
INTERIOR LIGHTING 



The problems encountered in applying light to building interiors have 
so many ramifications that the popular use of the term "illuminating 
engineering" often is restricted to such applications. This usage suggests 
the importance of this field as compared with most other phases of the 
lighting art and science. 

Usually, there are many correct solutions to a lighting problem. Modern 
standards call for the provision of both quantity and quality which are 
commensurate with the severity of the seeing tasks encountered by the 
occupants of a given area and which minimize the fatigue resulting from 
visual effort. -Lighting should enhance the over-all appearance of an 
interior. - 

- — To achieve these goals, bearing in mind that humans are mobile that 
their physical as well as mental ability to see varies as do their tastes, is a 
major objective of the illuminating engineering profession.— 
■— The solution of an interior lighting problem involves the following 
considerations : 

— Architecture. The physical structure in which light is to be applied 
determines to a large degree the form and disposition of the lighting 
facilities. --"It is reasonable to construct a building so that daylight may be 
used whenever available."" Daylight, however, varies with the geographical 
as well as the immediate location, and with the time of day, the season 
of the year, the weather and the presence of adjacent objects such as 
trees and buildings. Daylight is "free" but its transfer to the place of 
work at the time desired may be costly or impractical. Most buildings 
need an electrical -lighting system also.^ 

Though many of the graphs, formulas, and tables of this and other 
sections of the handbook are basic in lighting technology, lighting art is 
not subject to the same degree of standardization, since it is influenced in 
all its aspects by individual interpretation. 

—Architecture comprises the aesthetic as well as the physical and economic 
aspects of structures- This is equally true of lighting pthe two are not 
separable. Many buildings such as theaters emphasize aesthetic con- 
siderations to such a degree that these appear paramount to the casual 
observer. -Lighting is used by the architect in dramatizing the other 
features of his plan.- Aesthetic considerations are not always of such great 
importance, but they should never be ignored. 

1 — Function of a building. The function of a building or other structure 
greatly influences the way in which lighting is applied^ -A person when 
reading encounters the same type of visual task regardless of his location 
whether it be in a factory, in an office, or in a home, but such factors as 
economics, appearance, continuity of effort, and quality of results desired 
influence the lighting design developed for the reading area." Thus ap- 
plication techniques generally designated as industrial lighting, store 



Note: References are listed at the end of each section. 



10-2 I E S LIGHTING HANDBOOK 

lighting, office lighting, and so on have developed. Each of these is a 
synthesis of engineering theory, application experience, and consumer 
acceptance and desire in a particular field. Because these include more 
than an objective assessment of engineering considerations, it is necessary 
to relate the design of a lighting installation to the particular occupancy of 
the space it is to serve. 

- Lighting method. For most purposes it usually is impractical or impos- 
sible and undesirable to duplicate exactly natural lighting indoors either in 
illumination level, in spectral quality, or in distribution. Layouts of 
luminaires may be described as general, local, localized general, or supple- 
mentary. Five standard luminaire classifications, based on distribution 
characteristics, have been defined: direct, semidirect, general diffuse, 
semi-indirect, and indirect. The lighting facilities may be an integral part 
of the physical structure or, as is more often the case at present, may be 
attached to it. 

— Light source. The choice of light source, of luminaire characteristics, 
and of the system layout are closely interrelated in an application tech- 
nique. A method easily applied with one type of source may be equally 
applicable or most impractical with another. Frequently local conditions 
of vibration, ambient temperature, or dust and dirt influence light source 
operation, output, and maintenance and, indirectly therefore, the applica- 
tion technique.* (See also Section 6.) 

* Economics. Both initial and operating costs affect the design of a 
lighting system. There is no sharp line of demarcation between excellent 
and good lighting, between good and average, between average and poor. 
There is no easy way to predict the exact value of commercial or industrial 
lighting in terms of production, safety, quality control, employee morale, 
or employee health; or to weigh the importance of home lighting in dollars 
and cents Nevertheless, illuminating engineers must balance costs 
against the attainable results in developing any lighting design, relyingtoa 
great extent, at present, upon experience gained in the solution of compar- 
able problems if such is available. 

LIGHTING METHODS 

Today the elementary approach to the solution of lighting problems 
assumes small rooms (under 500 square feet) or bays (floor spaces resulting 
from the subdivision of a larger area by columns or other architectural 
supporting members), with ceiling heights between 8 and 14 feet. It 
assumes also that the illumination will be supplied from luminous areas 
small in proportion to the floor area they illuminate, suspended from the 
ceiling or surface mounted on ceiling or side walls. 

This approach is changing slowly. The trend toward large area sources 
that began prior to the availability of the fluorescent lamp was given 
increased momentum by its development Many large structures have 
clear floor spaces far in excess of 500 square feet. Nevertheless, the 
common approach follows a definite pattern. 



INTERIOR LIGHTING 



10 3 



Luminaire Layout 

The illuminating engineer has classified several types of lighting in- 
stallations according to luminaire layout as follows: 

General lighting is the name given to an arrangement of artificial sources, 
usually symmetrical in plan, which attempts to distribute light flux through- 
out a room to provide approximately uniform illumination on the working 
plane. Unless otherwise required or specified, the working plane is con- 
sidered to be 30 inches above the floor. The greatest advantages of 
general lighting are its independence of seeing task location and the relative 
simplicity of its installation and adjustment, ^he light distribution is 
similar to that provided out-of-doors. (See Fig. 10-1.) 



ts 




FIG. 10-1. General lighting. 

Localized general lighting utilizes luminaires mounted above the visual 
task which contribute also to the illumination of the surround. This 
compromise method utilizes the best points of general and local lighting 
and, at the same time, minimizes their limitations. Like any compromise, 
its success depends very much on whether the limitations of the funda- 
mental methods are important in the installation in question. (See Fig. 
10-2.) 

iJLocal lighting is the term applied to an installation of luminaires mounted 
at or near the location where illumination is required for a specific seeing 
task/ Occasionally, as in certain types of spotlighting, the result is local, 
although the equipment may be remotely placed. The greatest advantages 
of local lighting lie in its relatively low cost for high-illumination levels on 
.the task, and in its adjustment flexibility in the area of the seeing task. 
When used with general lighting it is called supplementary. (See Fig. 10-3.) 

Supplementary lighting may be provided by a variety of luminaire types 
used in conjunction with general lighting. The luminaires are installed 



10-4 



I E S LIGHTING HANDBOOK 




FIG. 10-2. Localized general lighting. 



' HP 




FIG. 10-3. Local lighting. 



so as to increase the illumination level on a seeing task and its immediate 
surround when it is not necessary or practicable to provide the same level 
over the wider areas covered by local, localized-general, or general- 
lighting installations. (See Fig. 10-4.) 



INTERIOR LIGHTING 



10-5 




FIG. 10-4. Supplementary lighting. 

Luminaire Classifications 

The manner in which light from a lamp is controlled by a luminaire 
affects brightness patterns, glare, and shadows through distribution and 
diffusion. Luminaires are classified by the International Commission on 
Illumination (I. C. I.) in accordance with the way in which they control the 
light as in Table 10-1. 

Wherever light is applied the directional component is important from 
architectural considerations. The play of light and shadow often estab- 
lishes the character of the structure; areas of contrasting brightness may 
indicate spaciousness, height, isolation, coziness, and so on. Thus the 
basic ways of directing light, even though they have evolved because of 
practical application considerations and are most often considered as a lu- 
minaire problem, should be viewed from an architectural standpoint as well. 

Table 10-1. I.C.I. Luminaire Distribution Classifications 

(See Fig. 10-5) 



CLASSIFICATION 


APPROXIMATE DISTRIBUTION OF 
LUMINAIRE LIGHT OUTPUT 

(percent) 




Upward 


Downward 


Direct 
Semidirect 
General diffuse 
Semi-indirect 
Indirect 


0-10 
10-40 
40-60 
60-90 
90-100 


90-100 
60-90 
40-60 
10-40 
0-10 



. 



10-6 I E S LIGHTING HANDBOOK 

Installations often are classified according to the light distribution 
characteristics of the luminaires employed: 

Direct lighting is the type of system in which light is distributed downward 
by the luminaire to the work plane only. (See Fig. 10-5.) Space between 
and above luminaires may be left dark by this type of distribution. Direct 
lighting, which was one of the first ways developed for applying electric 
illumination, provides maximum work -plane illumination. In many cases 
a direct lighting system is the least expensive. 

Disturbing shadows may result unless the area of the luminaires is 
relatively large or the luminaires are placed relatively close together. 
Shadows are at a minimum when the luminous area is largest, as with the 
so-called skylight or lighthood types. Direct and reflected glare may be 
distressing. In making installations care should be taken to avoid glare 
and excessive contrasts between the light source and its background. 

There are two direct-luminaire types: distributing and concentrating. 
The distributing types include reflectors and diffusers with surfaces of 
procelain-enamel, white baked synthetic enamel, diffuse aluminum, 
prismatic glass, and silver-mirrored glass. The "shielding angle" of a 
direct type fluorescent - lamp luminaire should be not less than 13 degrees 
below the horizontal. More shielding is desirable for filament-lamp 
equipment. The "cut-off angle" of a filament- lamp luminaire is meas- 
ured up from the vertical. Widespread light distribution which can be 
obtained also with aluminum, mirrored-glass, and prismatic-glass is 
advantageous in many applications in which the seeing tasks are in vertical 
or near- vertical planes. 

In most areas distributing units provide adequately uniform illumina- 
tion when they are spaced a distance not exceeding the mounting height 
above the floor; exceptions include areas of high ceilings or high bays. 

Concentrating direct-lighting luminaires include prismatic glass, mir- 
rored-glass, and aluminum reflectors. These are used in narrow high 
bays and in industrial craneways where it is necessary to mount the 
reflector at a height equal to or greater than the width of the area to be 
illuminated. In such areas, a concentrated beam directs light to the 
working area without excessive absorption by walls or unshaded windows. 
Spacing should provide uniform illumination over the working area. 
Similar luminaires, sometimes equipped with louvers, are used to provide 
supplementary lighting on specific work areas. 

Semidirect lighting is a natural evolution of direct lighting. Candle-, 
kerosene-, and~gas-flame luminaires were of this type. The design of 
semidirect luminaires sends 10 to 40 per cent of the light flux upward. 
This helps to tie together all parts of the room as an architectural whole, 
and to reduce the contrast between the luminaire and its background.- 
(See Fig. 10-5.) For the most part, luminaires in this class are of the 
open-bottom type, though some have closed bottoms of glass or plastic 
material. They are used for localized general lighting in many general- 
occupancy areas such as stores and also in service areas including corridors, 
stairways, washrooms, and locker rooms. 



INTERIOR LIGHTING 



10-7 




90% -100% 
DOWNWARD 



60%- 90% 
DOWNWARD 



40% -60% 
DOWNWARD 



FIG. 10-5. Characteristics of the luminaire distribution classifications established 
by the International Commission on Illumination (I.C.I.) . 

General diffuse lighting makes light available about equally in all direc- 
ti^ns^Brightness uniformity is improved, and luminaire-background 
con trasts a re reduced. Luminaires in this category include incandescent 
lamp enciosing-globe ancffluorescent-lamp types. (See Fig. 10-5.) 
Globes should be of a density sufficient to provide completely diffuse 
distribution. The surface area of luminaires should be sufficient to reduce 
their brightness to within one-twentieth that of the background. The 
"direct-indirect" luminaire that directs about half its output upward and 
the remainder downward with little or no horizontal component often falls 
into this classification. General diffuse lighting systems give more il- 
lumination for a specified wattage than do indirect or semi-indirect systems, 
binTcause more noticeable shadows and may cause both direct and reflected 
glare. 

Se mi-i ndirect lighting is a compromise between direct and indirect 
lighting. The direct component of semi-indirect luminaires is made as 
great (up to 40 per cent) as the installation efficiency requires and is 
balanced with the indirect component which may be as great (up to 90 
per cent) as the brightness and illumination uniformity of the installation 
requires. Both semi-indirect and indirect lighting light the ceiling and 
upper walls. (See Fig. 10-5.) 

In general, semi-indirect types have a larger utilization coefficient than 
do indirect units. More attention must be given to the factors of direct 
and reflected glare but less than to semidirect or direct types. Luminaires 
of this and other classifications are available in completely enclosed types, 



10-8 I £ S LIGHTING HANDBOOK 

which resist the collection of dust and dirt and are easily cleaned. Also 
there are styles that are open at both top and bottom so that only the 
upper surface of the lamps remains to collect dust and dirt. The reflec- 
tance of the ceiling shouM be maintained as high as practicable when semi- 
indirect or indirect luminaires are utilized. 

Indirect tig! ting is the type wherein the output of a luminaire is diffused 
and redistributed by a large intermediate surface (usually a ceiling). 
Indirect lighting is less efficient than most direct lighting because of the 
absorption of this redistributing surface, but it is a common means of 
getting very uniform levels of illumination. (See Fig. 10 5.) The 
permissible brightness of the intermediate surface and relatively low 
efficiency achievable limit its use. Ninety to 100 per cent of the light from 
indirect luminaires is first directed to the ceiling and upper wall areas, from 
which it is reflected diffusely to all parts of the room. Usually only enough 
light is emitted below the horizontal to raise the luminaire brightness to 
match that of the ceiling. 

One measure of the quality of lighting which a given source will produce 
is the angle subtended by the source at the point of work. With three- 
dimensional work tasks, particularly of a specular or semispecular nature, 
this factor is particularly important. The most common large-area source 
is an indirect-lighting system. In effect, the entire ceiling and upper wall 
areas become a light source. If the brightness is uniform and approxi- 
mately equal to that of the luminaires, with such a large area serving as a 
source of light, little direct glare is experienced at illumination levels up to 
about 50 footcandles. Shadows are practically eliminated and reflected 
glare reduced. As with semi-indirect luminaires, ceiling reflectance must 
be maintained high because at best this type of system is likely to be the 
least efficient. Specular and semi-mat-finished configurated ceilings have 
been developed for use with indirect-type luminaires to present reduced 
brightness at normal viewing angles. For many locations where indirect 
lighting is impractical there are available special luminaire types which 
produce somewhat the same effect. They consist of large luminous areas 
placed relatively close to the visual task, as in Fig. 10-6. The angle 
subtended by the luminaire is of the same order of magnitude as that 
subtended by an indirectly lighted ceiling. 

LIGHT AND ARCHITECTURE 

The typical luminaire may not be considered an architectural element 
by most illuminating engineers, but, regardless of terminology, lighting is 
so integrated with a building's use and appearance that it always should 
be given consideration in all stages of architectural design and decoration 
development Active co-operation betAveen architect and engineer is 
insurance against practical difficulties. *" Lighting can become the basic 
decorative or appearance motif, as well as a necessary working tool and an 
aid to comfort and safety in any interiorr*" 

Such structures as churches, theaters, and public buildings, usually can 



INTERIOR LIGHTING 



10-9 




FIG. 10-6. For maximum visibility of specular surface detail, general illumination 
is supplemented by light from large-area, low -brightness luminaires. 

not have their lighting classified simply as direct or indirect. They often 
are provided with more complex systems. Architectural planning of many 
of these structures involves traditional style and period considerations. 
The lighting design should be developed with full recognition of these 
considerations. Similar thinking sometimes is applied to other interiors, 
including homes, sales areas, and office and management areas of industrial 
plants. This architectural thinking encompasses hanging and surface- 
mounted as well as built-in luminaires and calls attention to the value of 
considering all types of lighting equipment integral parts of a structure, at 
least equal in importance to other elements. 

Luminaires should be related to the architectural motif of the building 
and should assist in carrying out an architectural plan. This is equally 
true of period and modern design. 



10-10 



I E S LIGHTING HANDBOOK 



Table 10-2. Styles and Lighting Effects of the Architectural Periods^ 



PERIOD 



Greek 700-146 B.C. 

Orders :Doric, Ionic, 
Corinthian 

Important build- 
ings: Temples 



Roman 146 B.C. -365 

A.D. 

Orders: Tuscan, 
Doric, Ionic, Co- 
rinthian, Com- 
posite 

Important build- 
ings -.Temples, ba- 
silicas, thermae 
(baths), palaces 



Early Christian 
300-900 a.d. 

Important build- 
ings: Basilican 
churches 



Byzantine 324 a.d. 
Important build- 
ings: Churches 



ARCHITECTURAL STYLE 



Column and lintel, with en- 
tablature. Harmony of de- 
sign so as to obtain perfect 
balance between horizontal 
and vertical elements. Per- 
fect proportion, simple 
decoration 



Column and lintel, with en- 
tablature. Arch developed. 
Vault and dome evolved. 
Elaborate decoration 



Column and lintel, with a 
long interior perspective. 
Occasional domes and ro- 
tundas supported on arched 
colonnades 



The dome on pendentives is 
the main feature of Byzan- 
tine architecture. In Ro- 
man architecture domes 
were used only over cir- 
cular or polygonal build- 
ings, but in Byzantine 
architecture domes were 
placed also over square 
structures. Here the ear- 
lier horizontal motif 
changes almost impercep- 
tiblv to a vertical motif 



NATURAL LIGHTING EFFECTSf 



Emphasis on the statue of the 
god or goddess to whom 
the temple was dedicated. 
Light was obtained from 
roof openings usually over 
the statue, or from clere- 
story openings, or from 
doorways. Temples were 
usually oriented so that the 
rising sun might light up 
the statue. Direction of 
incident light mainly from 
above, at oblique angles 

The Romans used windows 
extensive^. They obtained 
light by means of clere- 
stories, openings in the cen- 
ter of domes, or windows at 
the base of domes. Direc- 
tion of incident light 
mainly from above, at 
oblique angles. Light used 
to enhance the elaborate 
decoration and majestic 
proportions of interiors 

Oblique lighting from upper 
angles obtained through 
clerestories and window 
openings, usually small. 
Emphasis on altar obtained 
by columnar perspective as 
well as the convergent per- 
spective of windows in 
clerestories. Glass mosaics 
reflecting light often used 
for the high altar 

Lighting from upper angles 
obtained through windows 
at the base of domes. The 
dome being highly illumi- 
nated acted as a huge re- 
flector. Small glass and 
translucent marble win- 
dows prevented glare and 
added color to the interior. 
Brilliant mosiacs glowed 
with numerous subdued 
reflections. To relieve their 
flat wall decoration, the 
Byzantine builders ob- 
tained "depth" by means 
of arcades 



INTERIOR LIGHTING 



10-11 



Table 10-2— Continued 



PERIOD 



Romanesque 800- 
1200 A. D. 

Important build- 
ings: Churches, 
castles 



Gothic 1200 - 1500 

A.D. 

Important build- 
ings: Churches, 
monasteries, cas- 
tles, mansions, 
town halls 



Renaissance 1400- 
present day 

Important build- 
ings: Churches, 
castles, town 

halls, palaces, 
villas, chateaux, 
civic buildings 



Modern (twentieth 
century) 

All types of build- 
ings 



ARCHITECTURAL STYLE 



Massive Roman walls 
coupled with the round 
arch 



This aspiring style with its 
pointed arches definitely 
introduced the vertical 
motif. Solids prevailed in 
Roman architecture, but in 
Gothic architecture voids 
prevailed instead, since 
slender buttresses were 
used instead of massive 
walls 



The rebirth of classical ideals 
brought the ideal of archi- 
tectural harmony again in- 
to vogue. Buildings were 
so designed that the verti- 
cal and horizontal mem- 
bers obeyed the classical 
laws of proportion. For 
decoration Greek and 
Roman details were 
copied 



The twentieth-century style 
strives for structural logic. 
For skyscraper design the 
the vertical motif is 
emphasized. For smaller 
buildings the supporting 
steel structure is not cam- 
ouflaged but rather is inci- 
cated by simple "wall 
lines" and other decora- 
tive devices. Stone, glass, 
chromium, and other 
metals are used without 
elaborate ornamentation 



NATURAL LIGHTING EFFECTS! 



The effect of solemnity and 
vastness was produced by 
the contrast between great 
wall spaces and small 
windows. Such windows, 
single or grouped together, 
admitted rays of light 
through clerestories 

In churches the mood of so- 
lemnity was produced by 
the lofty, dimly illumin- 
ated ceiling, while long 
rays of light penetrated 
stained glass windows. In 
castles and manor houses 
larger windows than ever 
had been used before in 
domestic architecture be- 
came the vogue 

Lighting effects became more 
numerous to suit different 
types of buildings. Domes 
were supported on "drums" 
which were pierced with 
large windows. The dome 
lighting of the Byzantine 
period was revived and im- 
proved. The direction of 
incident light was still 
mainly from above, though 
lower windows also were 
enlarged. Windows be- 
came more numerous, and 
more light was sought than 
before 

Electrical illumination now 
is recognized as an archi- 
tectural medium. Modern 
lighting systems vary from 
the layout with outlets 
located with mathematical 
symmetry to the decorative 
system with light sources 
in arcades, columns, re- 
cesses, panels, cornices, 
coves, wall pockets, urns, 
etc. Luminaires differ 
widely in design and in 
material 



•D'Andrade. H. E., Lighting and Lamps, 1943. 

fSome use was made of flame sources (wooden torches, tapers, candles, and oil and gas lamps) even in very 
early periods. The design of luminaires in period interiors frequently follows the pattern established by the 
characteristics of these early lamps. 



10-12 I E S LIGHTING HANDBOOK 

Since the effect of daylight entering through openings such as ceiling 
apertures, skylights, and windows was utilized by even the earliest archi- 
tects, traditional designs may require a simulation of these elements. 
Luminaires designed in an attempt to recreate such effects should distribute 
their light in a similar manner. The movement of the sun in the sky 
produced a variation of effect during the day and from season to season, 
but, in general, some specific orientation was considered as a basis for 
architectural design. Once an orientation is selected, electrical lighting 
can readily duplicate (in many cases can surpass) natural -lighting effects 
because of its susceptibility to intentional variation and control. Struc- 
tural and ornamental details of a luminaire as well as its light-distribution 
characteristics should conform to the architectural motif. Some of the 
characteristics of the architectural periods are summarized in Table 10-2 
and in Fig. 10-7. 

Dual Installations 

Many plans for traditional and monumental interiors use two quite 
separate lighting systems. In a single interior one group of luminaires may 
be installed largely for appearance' sake, while the other group, wholely or 
partly concealed, provides utilitarian illumination. The architect may 
prepare aesthetic specifications for fixtures that appeal to him as good 
looking and appropriate, and establish the mounting height he knows is 
correct for the sake of appearance. At the same time, the engineer pro- 
vides most of the illumination needed by means of unobtrusively located 
utilitarian luminaires, placed where they will best provide the desired 
amount of light, of the proper color and other qualities. 

Built-in Luminaires 

Important departures from traditional design have helped to bring into 
being many interesting modern-lighting installations: 

An important contribution to the closer work of the two professions is 
the type of luminaire which, in conjunction with near-by ceiling or wall 
areas, provides wide bands, ribbons, panels, or disks of light, all of rela- 
tively low surface brightness, and with dimensions that the architect 
selects. 

Some of the common built-in lighting forms are described in the following 
paragraphs. Design and calculations data on some of these devices will be 
found in Table 8-12, (page 8-34). 

Luminous cornices are luminous panels located at beam or wall inter- 
sections with the ceiling (Fig. 10-8). 

Downlighting is a special term used to describe a direct-lighting system 
in which light emanating from above the ceiling line, controlled above or at 
the aperture by a recessed reflector, lens, or louvers, is projected through an 
aperture to the area to be illuminated (Fig. 10-9). 

Cove lighting is the term applied to sources concealed by a cove, ledge, 
or horizontal recess from which light is distributed over wide areas of 
ceiling space to be redirected downward (Fig. 10-10). 



INTERIOR LIGHTING 



10-13 




FIG. 10-8. Luminous cornices. 



10-14 



I E S LIGHTING HANDBOOK 



tS 




FIG. 10-10. Cove lighting. 



[NTERIOR LIGHTING 



10-15 



Luminous beams incorporate light sources in translucent plastic or glass 
forms (Fig. 10-11). When not illuminated they resemble steel, wood, or 
plaster beams. 

Luminous panels are large luminous areas resembling skylights (Fig. 10- 
12). 

Luminous coffers or troffers are recessed ceiling areas lighted by centrally 
or edge placed lamps (Figs. 10-13 and 10-14). 

Artificial skylighting utilizes luminous panels constructed and installed so 
as to imitate a natural skylight. In some cases light sources are mounted 
in a natural skylight for use on dark days or at night (Fig. 10-15). 

Luminous tubing usually describes hot- or cold-starting, low-current 
density fluorescent lamps or tubes which are used exposed or with very 
simple decorative or diffusing mediums to create light lines or patterns on 
ceilings or side walls (Fig. 10-16). 

Luminous elements include all of the forms mentioned as well as other 
unclassified combinations of lamps, diffusing mediums, and structural 
features that usually provide decorative effects and sometimes contribute 
substantially to the general illumination. 

Wherever the lighting equipment is to be planned as an integral part of a 
structure, it is necessary that the architect provide adequate space to 
house lamps and control equipment. Figure A-l , Page A-10 provides useful 
data for estimating the general illumination which may be provided in open 
interiors by a range of wiring capacities serving various types of light 
sources and luminaires. 




FIG. 10-11. Luminous beams. 



10-16 



I E S LIGHTING HANDBOOK 



•~'. 




FIG. 10-12. Luminous panels. 




FIG. 10-14. Troffer lighting. 




INTERIOR LIGHTING 



10-17 



^ 





FIG. 10-15. Artificial skylighting 





FIG. 10-16. Luminous tubing patterns. 



10-18 I E S LIGHTING HANDBOOK 

LIGHTING-APPLICATION TECHNIQUES 

Interior-lighting applications may be divided, for convenience in 
discussion, into six broad classifications: residence (including farm), office, 
store, school, public building, and industrial lighting. Although these 
classifications are not mutually exclusive and no sharp lines of distinction 
exist between them either in theory or in practice, their practical objectives 
may be quite different as, for example, the lighting of stores and offices. 
Physical differences (the average living room compared with an auto- 
mobile-assembly plant), emphasis on utility or decoration (the warehouse 
compared with the theater), and the variation of seeing task severity (the 
watch factory inspection department versus a night club corner table) have 
inspired the development of application techniques which are known as 
"current practice" in each of the six classifications. The specific tech- 
niques are discussed in some detail in succeeding subdivisions of this 
section. 

No summary of the considerations involved in any single interior is a 
sufficient guide for planning and designing all lighting installations. The 
following, however, should be weighed carefully in planning any lighting 
installation: 

Quantity of Illumination 

The primary standard of lighting effectiveness is the illumination level. 
Other factors held constant, increases in illumination level are accompanied 
by increases in visual acuity. With an acknowledgment of the limitations 
imposed by other factors, levels of illumination have been recommended 
by the Illuminating Engineering Society for many of the common seeing 
tasks encountered in each of the application fields. (See Table A-l, page 
A-l.) The tabulated illumination levels are neither minimums nor 
maximums, although they tend toward the former. They are found in the 
common practice of the day. which reflects a balance of many variables, 
including economic factors, convenience, and availability. The recom- 
mendations are reviewed periodically and when, because of new knowledge 
and practices, a change appears in order, a revised table is published. 

The scientific basis for appraising a seeing task involves four interrelated 
factors: (I) the size of the object to be viewed; (2) the brightness contrast 
between the object and its immediate background; (3) the time available 
for seeing; and (4) the average brightness of the object. Usually, the first 
three factors are constants in a specific lighting problem and only the 
fourth factor is chosen by a designer. Brightness equals the illumination 
(a controllable factor) times the reflectance of the seeing task. The im- 
portance of proper interpretation of illumination tables is evident. 

Quality of Illumination — Brightness Levels 

The provision of adequate levels of illumination does not guarantee 
comfort. Vision is not a mechanical process and therefore thought should 
be given to those factors that physically or psychologically contribute to 
the satisfaction of using the lighting. Such terms as "glare" and "shad- 



INTERIOR LIGHTING 10-19 

ows" are manifestations of these factors. A popular definition of glare is 
"light out of place." 

The Illuminating Engineering Society has established Brightness 
Standards for schools, homes, and offices based on the best data presently 
available. These standards are described on pages 10-52 and 10-76. 

The theories are discussed in Section 2. Data regarding calculation 
procedures are given in Section 8. 

Light Source Selection 

The characteristics of applicable light sources are important factors in 
lighting design and influence luminaire selection. Usually there are 
several light sources which can be applied in each lighting field. In some 
cases, however, a particular characteristic may be so important that a 
source strong in that capacity may meet the requirements best, despite 
other limitations. For example, a long-life lamp may be absolutely neces- 
sary for those places where replacement problems are very difficult. When 
there is a limited power supply or wiring capacity or very high power costs, 
a light source having a high over-all lumen-per-watt rating is particularly 
desirable. 

Luminaire Selection 

Before lighting calculations are made, a type of luminaire should be 
selected for preliminary consideration. The characteristics of different 
types of luminaires are described on pages 10-5 to 10-8. Luminaires 
are classified according to their light distribution characteristics and also 
according to their principal field of application, e.g., the industrial unit. 
This latter classification usually depends on the appearance, mechanical 
construction, and installation method and sometimes upon the electrical 
characteristics of the luminaire. 

In many cases, several types are available and the final selection may be 
made on the basis of overall cost and appearance. 

Luminaire Layout 

The determination of the illumination level and the type of luminaire 
permits consideration of the luminaire layout. Lighting levels (both high 
and low) and other factors occasionally restrict the type of equipment 
which may be chosen and its installation arrangement, but in most cases 
the advantages of a general, local, localized-general, or a general-plus- 
supplementary plan should be weighed. (See page 10-3.) 

The individual electric outlet layout plan is a basic method with incande- 
scent-lamp luminaires because of the symmetrical lateral light distribution 
characteristic of most equipment of this type and because of the economy 
and practicality of concentrating lamps of high rated wattages in single 
units. The most common plan consists of a symmetrical arrangement of 
one to four luminaires in a bay (or room). To a large extent, early fluores- 
cent installations followed this same technique. However, the present 
trend is to emphasize their linear characteristic and the result is a growing 
number of light patterns based on straight line elements. 



10-20 I E S LIGHTING HANDBOOK 

Even where fluorescent luminaires are suspended below individual 
electrical outlets, they may abut each other and be connected physically 
and electrically. Since common four-outlet-per-bay layouts usually 
call for 10- by 10-foot or 12- by 12-foot spacing, it is readily appreciated 
that combinations of 4 foot, 5 foot, and longer elements can bridge such 
spaces readily. Inherently, fluorescent lamps are of low lumen output per 
foot. The 40- watt lamp and its ballast consume together about 12 watts 
per foot. Thus, a greater luminous area and usually a larger number of 
lamps are needed to provide a given illumination level with fluorescent 
lamps than with the higher wattage incandescent lamps, despite the 
greater efficiency of the former. 

Lines and geometric patterns of fluorescent-lamp luminaires often are 
surface-mounted on the ceiling, suspended from it, or recessed in it. The 
low operating temperature of the fluorescent lamp, the value of diffuse- 
light distribution, and the harmonious architectural lines that such an 
approach creates, all have resulted in increasing emphasis on such patterns. 

MAINTENANCE OF LIGHTING 

Maintenance is a most important factor in the effectiveness of any 
lighting installation. In its broadest sense it includes everything connected 
with maintaining the output of a lighting system as near to its initial level 
as possible. Systematic maintenance plans should form a part of every 
installation design involving a large number of lamps. Today increasing 
recognition of the importance of maintenance is resulting in the develop- 
ment of specialized lighting-maintenance-service organizations. 

Incandescent-Lamp-Luminaire Maintenance 

In an incandescent-lamp luminaire, sometimes only the lamp itself is 
considered an essential operating part requiring regular replacement; 
however, the reflecting or other control medium also may be very important. 
When there is a factor of permanent or accumulative depreciation to be 
considered in these other parts (as contrasted with dirt which, hopefully, is 
considered temporary depreciation), provision should be made for their 
replacement also. Such depreciation is not necessarily a sign of poor 
design, although good design tends to minimize it. 

In addition to the dirt problem, the incandescent lamp, like other light 
sources, presents two other maintenance problems: output depreciation and 
failure to operate. Output depreciation is an inevitable condition of 
operation, although in some cases (e.g., series operation of street-lighting 
lamps) it may not be of concern from a maintenance standpoint because of 
compensating factors which are designed into the system. In designing 
installations, output depreciation is included in the original calculations in 
order to allow for the expected reduction in performance caused by operating 
conditions. 

When an incandescent lamp fails to operate, replacement is necessary. 
In many installations this is done on a "hit-or-miss" basis. In larger 



INTERIOR LIGHTING 10-21 

installations some attempt is made to schedule the procedure, to reduce the 
labor cost, and to provide less interference with other operations in the 
room. The system may be based on a periodic check and replacement, or 
on a scheduled replacement of all lamps in a particular area regardless of 
their operating or appearance status. The latter is termed group replace- 
ment and is based on the premise that the saving in cost of replacing lamps is 
greater than the value of the remaining light output in a large group of 
lamps after a certain number of hours of operation. This "smash point" 
usually is considered as falling between 60 and 80 per cent of rated lamp 
life. Generally it is assumed that the relatively few early failures that occur 
can be ignored, since they will not appreciably affect the average illumina- 
tion level. 

Fluorescent-Lamp-Luminaire Maintenance 

Fluorescent-lamp luminaires present problems similar to those of the 
incandescent-lamp type, although certain differences are noteworthy. 
First of all, the rated lamp life usually is longer, although usually there are 
many more lamps used in a given area because of the relatively low lumen 
output per lamp. Second, when luminaires are above head height, it is 
very difficult to replace lamps without lowering the luminaire or elevating 
the maintenance man. Third, the required circuit ballast and starting 
accessories, which must be maintained also, often are responsible for the 
inoperative lamp. Group replacement is feasible and highly desirable 
for many types of fluorescent installations. Cut-out starters are recom- 
mended for preheat-starting circuits, particularly those maintained on a 
group basis, since otherwise the constant on-and-off flashing characteristic 
of many early fluorescent lamp failures may not only be annoying to 
persons in the area but also harmful to ballasts. The larger the area 
lighted by a single tube or lamp, the more important it is to have a re- 
placement immediately. 

Depreciation 

Dirt depreciation is a function of the following variables: 

1. Room occupancy: some types of surroundings are dirtier than others. 

2. Luminaire design: particularly the dirt-collecting characteristics of 
reflecting and transmitting surfaces. 

3. Air movements in the room and in the luminaire. 

4. Nature of the dirt in the area. 

Dirt is a cause of poor appearance and poor sanitation as well as of 
inefficiency. To justify its cost, removing dirt should result (and usually 
does result) in improvements of equal or greater economical consequence. 
Figure 10-17 shows details that were calculated for a specific luminaire 
installation and fixed operating conditions. For any luminaire and ap- 
plication condition similar graphs can be prepared in which the loss of light 
caused by a particular percentage of dirt is evaluated in terms of over-all 
operating costs and the cost of each cleaning. If in a given time the loss of 



10-22 



I E S LIGHTING HANDBOOK 





LAMPS REPLACED WITH NEW 
LAMPS OF PROPER VOLTAGE 



100 % 



t 80 



60 



-. 40 



^ 20 



4 



LAMPS AND 
REFLECTORS CLEANED 

1 



REPAINTING 



ILLUMINATION 
AS FOUND 






tf'.V 






FIG. 10-17. Increased reflec- 
tances, improved brightness 
ratios, and higher illumination 
levels may be obtained by sim- 
ple maintenance procedures. 





light (evaluated in dollars) is greater than the cost of cleaning, it is eco- 
nomically sound to decrease the time interval between cleanings. As the 
individual cleaning cost increases, a longer period between cleanings is 
justified. 

The cost of cleaning will vary depending on local labor rates; on the 
luminaire design, its mounting height and location, and the physical 
difficulty of reaching it and of cleaning it in place, or of disconnecting it for 
cleaning at floor level or elsewhere; and upon the possible interruption in 
other operations that the operation may make necessary. 

Cleaning Materials, Equipment, and Procedures 

Most cleaners will not harm glass surfaces. However, care must be 
taken in cleaning metal reflectors, since both alkali and acids may attack 
the metal, causing roughness, pitting, etc., and thus reduce the reflectance 
of the surface and cause it to collect dirt faster. Wax or wax-emulsion 
cleaners leave a thin wax film on a surface which eases subsequent cleaning 
and helps to retain high reflectance. 



INTERIOR LIGHTING 



10-23 




FIG. 10-18. A luminaire mainte- 
nance truck or wagon with compart- 
ments for cleaner, rinse water, rags 
and lamps. 



When reflectors or glassware can be taken down for cleaning, the following 
procedure is recommended : 

1. Immerse parts in a cleaning solution and scrub with sponge or 
soft brush. 

2. Kinse in clear warm water. 

3. Do not immerse lamp bases or any electrical connections. 
When reflectors or glassware cannot 

be taken down, wash with a cleaner 
that requires no rinsing, and wipe off 
excess moisture with a clean cloth. 

A cleaning truck is shown in Fig. 
10-18. 

Practical methods of reaching lighting 
equipment. Table 10-3 will aid in the 
selection of suitable lighting mainte- 
nance equipment. 

Pole lamp-changers. The simplest 
type of lamp-changing device is the 
clamp grip mounted on the end of a 
pole as shown in Fig. 10-19. In many 
industrial plants with installations of 
open-bottom, vertically-mounted, in- 
candescent-lamp luminaires, pole- 
changers are used between periods of 
regular maintenance for emergency 
lamp replacement. For recessed reflec- 
tor lamps this device is particularly 
well suited since, no other special main- 
tenance equipment will be required. 

Disconnecting and lowering hangers. 
Disconnecting and lowering hangers 
offer many advantages for safe, eco- 
nomical maintenance of lighting equip- 
ment. With such hangers the lumi- 
naire can be lowered to the floor by 
means of a permanently fastened chain 
or cable. (See Fig. 10-20.) Usually 
the chain is carried to some convenient 
location where it is out of the way until 
needed. When the reflector is lowered 
the electrical circuit is broken. After the reflector has been cleaned and 
relamped, it is pulled back into place, where it automatically locks into 
position, reestablishing the electrical circuit. 

Steplodder. For relatively low mounting heights, stepladders are used 
because of their convenience and portability. Clips and hooks which hold 





FIG. 10-19. A pole-type lamp-changer. 



10-24 



I E S LIGHTING HANDBOOK 



Table 10-3. Typical Maintenance Devices for Various 
Luminaire Mounting Heights 



TYPE OF EQUIPMENT 



LUMINAIRE MOUNTING HEIGHT 



Pole lamp-changers 

Disconnecting hanger 

Stepladder 

Straight ladder 

Portable maintenance platform 

Crow's-nest ladder 

Telescoping platform, elevating tower, etc. 

Catwalk or truss (fixtures swing in) 

Crane or Relamping bridge 




12 to 18 ft 


18 to 30 ft 


Above 30 ft 


X 


— 





— 


X 


X 


— 


— 


— 


X 


— 


— 


X 


X 


— 


— 


X 


— 


X 


X 


— 


— 


X 


X 




X 


X 




and lSv-erin^crank ° nneCting ^ lowering han S ers - Inserts show disconnect housing 



INTERIOR LIGHTING 



10-25 




FIG. 10-21. Luminaire-maintenance 
ladders. 



spare lamps and cleaning rags enable 
a man to do an entire cleaning and 
relamping job with one trip up the 
ladder. (See Fig. 10-21.) Where 
reflectors are removable the following 
procedure is recommended: 

1 . Clean the spare reflector (or the 
set of light control parts); carry the 
clean parts up the ladder. 

2. Hook the clean reflector to the 
ladder while disconnecting the dirty 
one. 

3. Install the clean reflector. 

4. Bring down the dirty reflector; 
clean and use it in similar fashion at 
the next outlet. 

In many cases where the entire instal- 
lation is cleaned at frequent intervals 
specially designed cleaning trucks such 
as shown in Fig. 10-18 are used. 
Three compartments are useful: one for cleaning solution, one for rinse 
water, and one for clean rags. If convenience outlets are installed through- 
out the area, both clsaning solution and rinse water can be kept hot with 
immersion heaters. 

Wherever possible, luminaires should be cleaned at floor level because a 
more thorough job can be done, greater safety is assured, and there is less 
possibility of splashing cleaning solution or rinse water where it is not 
wanted. 

Straight ladder. In some cases ordinary ladders can be modified slightly 
to meet specific reflector mounting conditions. For example, a lightweight 
brace mounted on the end of a ladder, when placed against a beam, may 
provide the maintenance man more convenient access to the luminaires. 
(See Fig 10-21.) 

Portable maintenance platform. These are used where there are a great 
many luminaires at a given mounting height. (See Fig. 10-22.) These 
platforms are equipped with castors and the smaller ones can be made so 
light in weight that one man can handle them without difficulty. The use 
of such platforms, particularly with continuous-row, fluorescent-lighting 
installations, permits a man to reach several luminaires safely without 
changing the platform position. Occasionally, in industrial plants with 
regularly spaced aisles and equipment serviced from the floor, the platform 
may be designed to span the spaces bteween adjacent aisles. 

Crow's-nest ladder. This type of ladder attached to a truck body has been 
used for street-lighting maintenance and may be adapted to interior-lighting 
maintenance in large areas with wide aisles. Trucks are designed -with a 
short wheel base and short turning radius to permit a man on the ladder to 
reach the entire lighting installation. The crow's-nest ladder shares with 
other movable platforms the ability to reach luminaires that are located 



10-26 



I E S LIGHTING HANDBOOK 




FIG. 10-22. Portable maintenance platforms: 
nest ladder, c. telescoping type. 



fixed height type. 



over machinery and other obstacles, since the ladder may swing out at an 
angle over the side or back of the truck. Hooks and damps should be 
attached to the ladder (see the discussion of stepladders) to hold the re- 
quired spare lamps and cloths. Ladders of this type provide a secure 
platform to which a safety belt may be attached. 

Telescoping platform, elevating tower, etc. Telescoping devices have the 
advantage of small size when the various extensions are nested together, 
which permits their passage through low doorways, facilitates storage, etc. 
They can be designed to reach nearly any desired height. Outriggers which 
may be folded into the frame while it is in transit give this type of device 
added stability. (See Fig. 10-22.) 

Catwalk or truss. High-bay installations can be designed with luminaires 
mounted near trusses or specially designed catwalks to which they can be 



INTERIOR LIGHTING 



1027 



STOP-STRIP 



-->, \ HOLDS / <. 

I \ \ REFLECTOR / / I 





"CATWALK ON CRANE 

b 

FIG. 10-23. Provision for luminaire maintenance sometimes is provided in build- 
ing or machinery installation plans. Luminaires may be reached conveniently from 
(a) catwalks or trusses, (b) cranes, or (c) monorail cars. 

pulled with a short hook and secured for cleaning. (See Fig. 10-23a.) This 
permits a maintenance man to clean and relamp conveniently and safely. 
The hanger should be designed so that a man may perform his work com- 
fortably and rapidly and with a minimum of physical effort. For example, 
reflectors at catwalk floor level require bending or kneeling and increase the 
possibility of dropping cleaning materials or lamps. A kickplate at the 
edge of a catwalk will catch many things that otherwise might roll off. 

Crane. Cranes such as that shown in Fig. 10-23b are utilized for lighting 
maintenance in many high-bay areas. Attention should be given in plan- 
ning the original lighting layout and crane facilities to permit convenient 
access to the reflectors. If the crane is designed to pass just under the 
lighting equipment, it is desirable to place an auxiliary platform below the 
maximum elevation of the crane so that the fixtures are approximately 6 
feet above the platform. Thus the maintenance man can clean the reflector 
conveniently and reach the other parts and the wiring. If the roof is a 
considerable distance above the crane, the reflectors should be suspended 
within 6 feet of the crane platform upon which the man will stand. 

Relamping bridge. In high ceiling areas, where cranes (if they are 
available) aie not to be used for lighting maintenance or where there are 
overhead monorails, relamping bridges, or cars such as that shown in Fig. 
10-23c may be used. These are maintenance platforms designed for ceil- 
ing suspension. They may be towed into place; they may be individually 
operated on the monorail system; or they may be placed in position by the 
crane. They have been found satisfactory for simultaneous maintenance of 
relatively large areas. 



10-28 I E S LIGHTING HANDBOOK 

LIGHTING AND BUILDING CODES 

The Illuminating Engineering Society is the recognized authority in the 
lighting field and has published many Recommended Practices. Several are 
reproduced in condensed form in this handbook. 

The complete texts of the following may be obtained from the I.E.S. 
General Offices, 51 Madison Avenue, New York 10, in booklet form: 

American Standard Practice of School Lighting. 

Recommended Practice of Office Lighting. 

Lighting Practices for Stores and Other Merchandising Areas. 

Recommended Practice of Home Lighting. 

American Recommended Practice of Industrial Lighting. 

American Standard Recommended Practice of Street and Highway Lighting. 

LIGHT AND AIR-CONDITIONING 

Since any light source adds to the total heat in the interior in which it i s 
operated, to the extent of 3.413 British thermal units per hour per watt of 
power consumed, it is evident that there is some relation between lighting 
and room temperatures. Tons of air conditioning = Btu per hour/12,000. 
However, the sensation of human comfort, which is not of necessity directly 
related to room temperature, is the important factor in air-conditioning, 
rather than the absolute room temperature. 

A light source operated in an interior adds two types of heat, usually 
termed sensible and radiant heat. Sensible heat is that which is added 
directly to the air through conduction or convection. It results in a rise 
in the indicated room temperature. Radiant heat is that added through 
radiation. Radiant heat is turned into sensible heat only by interception 
(as by opaque objects such as furniture and the human body, or by air to a 
very minor degree). 

Light sources emit invisible as well as visible radiant energy. Wave- 
lengths between 0.34 micron (the lower limit of ordinary window-glass 
transmission) and 3 microns are absorbed or reflected to a varying degree 
throughout this range by the human skin; wavelengths above 3 microns 
are almost entirely absorbed. A large percentage of incident energy in 
wavelengths greater than 4 microns is absorbed by window glass. 

The relative proportions of sensible and radiant heat are not the same 
for all light sources, nor does the efficiency of a lamp bear any direct relation 
to such values. For example, a sodium lamp may have a rated output of 
50 lumens per watt, as may a fluorescent lamp. The former, nevertheless, 
emits slightly more heat per watt because its efficiency is a result of spectral 
energy concentration near the wavelength of maximum luminosity. A 
smaller proportion of the total power input goes into the visible sodium 
line than goes into the continuous visible spectrum of a 504umen-per-watt 
fluorescent lamp, and a larger proportion therefore is converted into heat. 

A fluorescent lamp with the same approximate color temperature as an 
incandescent lamp is more efficient and "cooler" to the touch. The 
important fact is that a lower total wattage load is needed to produce a 



INTERIOR LIGHTING 10-29 

desired illumination level with fluorescent lamps than with incandescent 
lamps. The ratio of radiant to sensible heat for fluorescent lamps therefore 
is less than that for incandescent lamps providing the same illumination 
level. (See Fig. 6-31, page 6-37.) 

Certain relationships between heat and the human reaction to it must be 
understood in order to appreciate the relationship of light to air-condition- 
ing, or of room comfort to temperature and humidity. Table 10-4 indi- 
cates the temperature rise resulting, under certain conditions, from various 
lighting loads in a small office. Temperature rise in a room is a result of 
many things: primarily heat transfer through walls, heat transfer with air 
changes, heat radiation that accompanies sunlight, heat emitted by human 
occupants, and the heat of the occupational process. Artificial illumina- 
tion, sunshine, and process heat are the most noticeable heat sources. In 
many offices and stores direct sunlight is eliminated and there is no obvious 
process heat. It is believed more attention than is justified is directed to 
the electrical illumination. Today 10 watts per square foot is higher than 
the average lighting load, and about 3 degrees Fahrenheit is the minimum 
effective-temperature-difference perceptible to the average human, other 
conditions being constant. 

Humidity. Temperature is measured by a thermometer which, if not 
otherwise specified, is of the dry -bulb type. However, since the human body 
regulates its temperature to retain the normal 98.6 degrees Fahrenheit by 
skin evaporation as well as by radiation and convection, and since the rate 
of such evaporation depends on the humidity of the air and continues from 
the normal, active human being, regardless of outside conditions, the sensa- 
tion of heat as interpreted by human comfort is a function of air water con- 
tent as well as of absolute temperature. Air (and in fact, any gas) has the 
property of sharing space with water vapor up to a specific amount. For 
any given temperature, this amount of water per unit volume- is called the 
saturation point; the related temperature is called the dew point. For 
example, at 70 degrees Fahrenheit and at sea-level pressure (29.921 inches 
of mercury) air will hold 0.01865 ounce of water per cubic foot. The 
variation below this theoretical ideal, which is rated 100 per cent, is called 
relative humidity. With reference to the average human skin, values over 90 
per cent are called extreme, those between 60 and 90 per cent humid, between 
40 and 60 normal, and under 40 per cent dry. Such generalizations are 
approximate only, since ambient temperature, activity of the individual, air 
movement, and so forth make appreciable differences in the apparent sensa- 
tion which is experienced. 

Relative humidity is measured by comparison between wet-bulb and dry- 
bulb thermometers. The wet-bulb type has its bulb area covered by a wet 
cloth. In use, air movement past the wet bulb is required toencourage 
evaporation. Evaporation tends to lower the reading below that recorded 
by a dry-bulb instrument. The relation between the two temperatures is a 
measure of relative humidity. If the wet-bulb thermometer shows the same 
temperature as the dry-, it indicates that no water has evaporated and there- 
fore that the humidity is 100 per cent. 



10-30 



I E S LIGHTING HANDBOOK 



Table 10-4. Temperature Rise Over a 7-Hour Period Attributed to the 

Electrical-Lighting System in a Two-Window Office 

(300-Square-Feet Floor Area)* 



ELECTRIC POWER DELIVERED 

TO LIGHTING SYSTEM 

(watts per sq ft) 


TEMPERATURE RISE 

(degrees fahrenheit)t 








Windows and Transom Open 


All Openings Closed 


2 


0.5 


1.5 


4 


1 


3 





1.25 


4.5 


8 


1.8 


6 


10 


2.25 


7.5 


12 


2.6 


9 


14 


3.1 


10.5 


16 


3.5 


12 


18 


4 


13.5 


20 


4.3 


15 



•Sharp, H. M., "Lighting and Air Conditioning," Lighting and Lamps, April 1946. 

tThe test-room temperature rise shown here has been corrected by comparison with data on the "control" 
room without electric lighting so that the influence of inside and outside temperatures and wall materials is 
minimized. 

Comfort limits. The relationship between comfort and temperature and 
humidity has been determined by a study based on human experiences and 
voiced reactions. A summary of such observations is compiled in Fig. 10- 
24. The chart indicates that the effective temperature is a few degrees below 
the dry-bulb temperature, the amount below being indicative of the dryness 
of the air. It shows also that a person does not on the average notice 
changes of humidity or temperature when their net result is a change in 
effective temperature under 3 degrees Fahrenheit. The figure varies to some 
extent with absolute values, climate adaptation, occupational activity, and 
individual human sensitivity. 

The data of Fig. 10-24 apply to still-air conditions with which are associ- 
ated the highest effective temperatures. Air movement increases water 
evaporation from the skin and reduces the effective temperature. 

Lighting load on an air-conditioning system. An important point in the 
design of an air-conditioning system is that increasing the lighting level by 
doubling the watts per square foot is not likely to result in the requirement 
of a refrigerating unit of doubled capacity. Table 10-5 indicates that from 
9 to 24 per cent of the air-conditioning load for a variet}* - of interiors may be 
attributed to lighting. 

By raising skin temperature above the comfort zone, radiant heat in some 
cases may cause discomfort when the air-temperature-humidity relationship 
is within the zone (Fig. 10-24). In other cases, when the air-temperature- 
humidity relationship is below the comfort zone, radiant heat may provide 
comfort by raising the skin temperature into the zone. 

The rate of heat loss by radiation depends on the exposed surface of 
the body and upon the difference between the mean surface temperature 
of the surrounding walls or other objects, called mean radiant temperature 
(mrt).* 



'Heating, Ventilating, Air Conditioning Guide, 19J7, American Society of Heating and Ventilating Eijgi- 
peers, New York, 



INTERIOR LIGHTING 



10-31 



90 80 




65 70 75 80 85 90 

DRY BULB TEMPERATURE IN DEGREES FAHRENHEIT 



FIG. 10-24. Still-air comfort chart of the American Society of Heating and Ven- 
tilating Engineers.* 

Note: Summer and winter comfort zones apply to inhabitants of the United States 
only. Application of the winter comfort line is further limited to rooms warmed by 
central-heating systems of the convection type. The line does not apply to rooms 
heated by radiant methods. Application of the summer comfort line is limited to 
homes, offices, and the like where the occupants become fully adapted to the arti- 
ficial-air conditions. The line does not apply to theaters, department stores, and the 
like where the exposure is less than 3 hours. The optimum summer comfort line 
shown pertains to Pittsburgh and to other cities in the northern portion of the United 
States and southern Canada, and at elevations not in excess of 1,000 feet above sea 
level. An increase of approximately 1 degree effective temperature should be made 
per 5-degree reduction in north latitude. 



* Heating, Ventilating, Air Conditioning Guide, 1947 
gineers, New York. 



American Society of Heating and Ventilating En- 



10-32 



I E S LIGHTING HANDBOOK 



Available data indicating the effect on comfort of mean radiant tempera- 
ture is less conclusive than that available on effective temperature, but it is 
accepted that a change of G degrees in mean radiant temperature is the 
minimum significant perceptible difference. The problem is complicated by 
the distinct differences in sensitivity of different parts of the body. The 
backs of the hands and the face are the most sensitive parts. (See Table 
10-6.) 

Thus, under certain conditions, local lighting installations may be the 
cause of some radiant-heat discomfort despite a comfortable air-tempera- 
ture-humidity relationship. Since the heat removed from the skin by air 
convection or conduction may not equal that added by a concentrating 
reflector, a local temperature rise may result. Hot ceilings, walls, or floors 
may be the cause of a similar phenomemon. 

Table 10-5. Relative Values of Various Contributing Loads Given 
in Per Cent of Total Cooling Load* 



CONTRIBUTING LOAD 



Lighting 
Solar radiation 

through windows 
Conducted heat 
Occupants 
Outside air 
Miscellaneous 



PER CENT OF TOTAL COOLING LOAD 



Offices 



17 

111 

17 
14 
26 
10 



Apparel 
Stores 



24 
6 

26 
18 
22 

1 



Depart- 
ment 
Stores 



24 

7 

15 

20 

28 

6 



Drug 


Beauty 


Stores 


Shops 


12 


9 





3 


23 


26 


32 


15 


23 


15 


10 


33 



Restau- 
rants 



9 
2 

12 

26 
29 
•>■> 



Small 
Shops 



19 
4 

28 
14 
25 



•Sharp, H. M., "Lighting and Air Conditioning," Lighting and Lamps, February 1946. 



Table 10-6. Relationship Among Mean Radiant Temperature (MRT), 
Flux Distribution Characteristics of Luminaires, Power Load, and 
Illumination Level in Various Interiors* 



AREA 


LUMINAIRE 


LAMP " 


WATTS 

(sqft) 


MAX 
HORI- 
ZON- 
TAL 
FOOT 
CAN- 
DLES 


MRT 

AT 
POINT 

OF 
MAX 
FOOT 
CAN- 
DLES 


MRT 
PER 
FOOT 
CAN- 
DLE 


MRT 

OF 

TOTAL 

IN- 
TER- 
IOR 


Private office 


Indirect 


Incandescent 


4.5 


24 


1.4° 


0.06 


0.8° 


Private office 


Direct-indirect 


Incandescent 


3.5 


60 


0.25 


.004 


0.8 


General office 


Indirect 


Incandescent 


8.3 


33 


2.0 


.06 


2.0 


General office 


Luminous indirect 


Incandescent 


5.0 


40 


3.0 


.07 


4.0 


General office 


Luminous indirect 


Incandescent 


3.0 


18 


1.0 


.055 


1.0 


Drafting room 


Indirect 


Silver bowl incand. 


5.0 


30 


3.0 


.1 


3.0 


Retail store 


Indirect 


Incandescent 


4.5 


10 


1.0 


.1 


1.0 


Dept. store 


Indirect 


Incandescent 


2.6 


15 


1.0 


.06 


1.5 


Variety store 


Indirect 


Incandescent 


6.25 


42 


1.5 


.04 


1.8 


Variety store 


General diffuse 


Incandescent 


3.3 


39 


3.5 


.09 


6.5 


Industrial plant 


Direct 


Silver bowl incand. 


4.3 


39 


1.5 


.04 


1.0 


Industrial plant 


Direct 


Incandescent and 
mere, vapor 


2.65 


64 


2.8 


.044 


2.0 


Local lighting 


Direct 


Incandescent 


— 


.25 


0.006 


— 


— 



•Sharp, H. M., "Lighting and Air Conditioning," Lighting and Lamps, June 1946. 



INTERIOR LIGHTING 10-33 

RESIDENCE LIGHTING 

The rooms of a home are expressions of the method of living, taste, ac- 
tivities, and so on of a family or an individual. Residential-lighting design 
is a compromise between individual taste, tradition, decoration, and 
practical engineering. The recommendations presented here have been 
selected and condensed from the I.E.S. Recommended Practice of Home 
Lighting. 

The lighting of living room, dining room, and kitchen in farm homes may 
differ from that of similar areas in urban residences because the occupancy 
may be somewhat different. In general, however, residential space is 
utilized today in urban and rural areas for about the same purposes. Farm 
buildings which may or may not be directly connected with the farmhouse 
require good illumination also. (See the following section.) 

Fundamentals of Residence Lighting 

Despite the fact that distribution curves, symmetrical spacings, luminaire 
efficiencies, and similar data at present are not always considered essential 
in residence-lighting design, the basic factors of quantity and quality of 
illumination still should be considered both in the design of home-lighting 
equipment and in its application. As in any other interior, lighting should 
be planned objectively to simplify seeing tasks, and subjectively to increase 
human comfort. Similarly, it should be so co-ordinated with the archi- 
tectural detail and interior decoration as to blend inconspicuously with it 
and to add interest to it. Stated in direct reference to the home, the 
broad lighting considerations that should be used as a guide are : 

1 . The attainment of the recommended illumination levels for the many 
visual tasks common to the home. 

2. The provision of a quality of illumination that ensures seeing comfort 
for the occupants. 

3. An understanding handling of the color of the light sources utilized. 

Quantity of illumination. Varied seeing tasks in the home require dif- 
ferent quantities of illumination and brightness ratios. Recommended 
illumination levels are included in Table 10-7. Typical luminaires are 
shown in Figs. 10-25 to 10-31. 

Quality of illumination. To ensure comfort in the use of the recom- 
mended illumination on seeing tasks, it is essential that the resultant task 
brightness not greatly exceed that of the background against which it is 
viewed. This requires such a distribution of the light within a room that 
the room is free from glaring bright spots and deep shadows. Glare too 
often is associated only with unshaded lamps. Luminaires may be sources 
of discomfort also if they are much brighter than the surface against which 
they are viewed. Usually, comfortable, low-brightness ratios may be 
attained by distributing light uniformly throughout a room. Low- 
brightness luminaires are particularly important in living rooms, dining 
rooms, and bedrooms. In these rooms persons often spend many hours in 



10-34 



I E S LIGHTING HANDBOOK 



seated positions, which may bring the luminaire within their view. It is 
not suggested that a room used for social conversation or other "nonseeing" 
activity be illuminated to eliminate all shadow and contrast. Such a room 
would be unattractive. However, deep shadows may cause unnecessary 
eyestrain and fatigue when the room is used for difficult seeing tasks, rather 
than for relaxation and conversation. 

Relationship between ceiling, wall, and floor color and reflectance, and light 
utilization and appearance. The utilization of light within a room depends 
on the wall, floor, and ceiling reflectances. A room is likely to appear 
attractive to most people when the ceiling has the highest, the floor the 
lowest, and the wall an intermediate reflectance. The following reflectances 
are typical of good practice today: ceilings between 65 and 80 per cent; 
floors between 10 and 20 per cent; and walls between 35 and 55 per cent. 
In rooms where visual tasks are difficult the higher values are better. Wide 
variations from these values often are used in rooms where decorative 
treatment is of paramount interest and severe visual tasks are not 
performed. 

Table 10-7. Recommended Illumination Levels for the Home* 



AREA AND VISUAL TASK 



GENERAL LIGHTING FOE : 

Entrance hall, stairways, and stair landings 

Living room, library, sunroom 

Dining room 

Kitchen 

Bedroom 

Bathroom 

LIGHTING FOR: 

Kitchen (work counter, range, and sink) . . . 

Dressing-table mirrorf 

Bathroom mirrorf 

Laundry (ironer, ironing board, or tubs) . . . 

Work bench 

Reading 

Prolonged periods (smaller type) 

Casual periods (larger type) 

Sewing 

On dark goods, fine needlework 

Average sewing (prolonged) 

Average sewing (periodic) 

Writing 

Children's study tablej 

Game tables 

Card table 

Ping-pong 



FOOTCANDLES 

MAINTAINED IN 

SERVICE 



5 
5 

5 

10 

5 

5 



40 

20 
40 
40 
40 

40 
20 

100 
40 
20 
20 
40 

10 
40 



*The values given for general lighting are intended to minimize brightness ratios between the illuminated 
visual tasks and the surround. Where difficult seeing tasks are not involved, the values listed aim to assure 
safe passage, eye comfort, and charm. 

The given values for typical home tasks are chosen for persons with normal vision, giving proper considera- 
tion to such matters as cost and practical attainment. They do not represent the optimum, since under some 
conditions more light may be necessary and desirable, and often more light is attainable. 

The values listed may be attained by either fixed or portable luminaires, or by a combination of the two. 

tTo be delivered on both sides of the face. 

JOften a dining-room table, 



INTERIOR LIGHTING 10-35 

The appearance of an object is influenced by the color of the incident 
light. For example, the monochromatic yellow color of light from the 
sodium lamp is not suited to home lighting because, when they are illumi- 
nated by this light, all objects which do not have some yellow in their 
surface appear black, and the yellow in others is so emphasized as to distort 
completely the intended appearance. Because most homes are at least 
partially illuminated by direct sunlight and skylight during the day, in- 
terior colors often are selected for their outdoor appearance. A daily 
variation in appearance is caused by hourly changes in the orientation of 
the sun, by weather variations, and by the spectacular sunrise and sunset 
hues. Also, since the color of light from electric lamps is uniform and does 
not exactly duplicate either sunlight or skylight, another variation is 
introduced. Generally speaking, of the light sources used in homes the 
300-watt incandescent lamp is the one which produces light most similar to 
direct sunlight. Light from daylight fluorescent lamps is most similar to 
that from a clear blue sky; and light from white fluorescent lamps is some- 
what similar to sunlight and skylight combined. 

By comparison, light from incandescent lamps emphasizes red and 
yellow colors and tones down the greens and blues; light from fluorescent 
lamps emphasizes green and blue colors and tones down the reds and yel- 
lows. (See Section 4.) With either type of lamp, high chromas in the 
light-controlling materials of luminaires or on large wall areas should be 
avoided if it is desired to retain an outdoor appearance. 

It should be realized that in a store the appearance of household acces- 
sories is influenced in a similar manner by the illumination and decoration. 
A considerable change in appearance may be noted if the home conditions 
under which the accessory is to be used or displayed differ in appearance 
from those of the store. 

The usual lighting requirements of each major room of the average 
home are discussed on the following pages. The recommended luminaire 
light distribution characteristics should be adhered to. However, deco- 
rative detail is a matter of taste and market supply. 

Entrances, Halls, and Closets 

Architectural treatment dictates the placement and type of entrance 
luminaires. Brackets that provide downlight on steps (Fig. 10-25a) 
preferably are placed at each side of the door. Often a single bracket above 
the door harmonizes better with the architectural design but may prevent 
seeing clearly the face of the caller. On an attached porch, a suspended 
lantern (Fig. 10-25c) should be placed on the porch ceiling so that the 
steps are lighted for safety. Clear glass panels in brackets or in a lantern 
should be avoided, since lighted lamps behind clear glass may prove more 
blinding than helpful. When a doorway is slightly recessed, a recessed 
element (60- or 100-watt lamp) may be inset inconspicuously in the soffit 
above, with a pleasing result. Use of a 150-watt projector floodlamp 
(Fig. 10-25g) or a 100-watt lamp in an angle reflector set under the eaves 



10-36 



I E S LIGHTING HANDBOOK 




FIG. 10-25. Typical recommended luminaires for entrances, halls, and closets. 
a. Lantern bracket, b. Semi-indirect, c. Ceiling lantern, d. Recessed house num- 
ber, e. Attached house number, f. Semidirect. g. Projector lampholder. h. Gen- 
eral diffuse lantern. 



and switch-controlled from the house, will provide ample protective 
lighting between the garage and the house as well as yard and garden 
lighting. 

A lighted house number may be incorporated in the entrance lantern, in a 
separate recessed box (Fig. 10-25d) located in the house wall or steps, or in a 
special applied box connected to the door-bell circuit (Fig. 10-25e). The 
size of numerals is important ; for clear visibility up to 75 feet, they must be 
at least 3 inches high with a half-inch stroke. 

In halls with open stairways, lantern-type luminaires (Fig. 10-25h) often 
are used. Their scale and design should fit the interior. They should be 
placed to illuminate adequately for safety on the stairs. The type shown 
in Fig. 10-25b must be mounted close to the ceiling in order to shield the 
lamps from the view of persons descending stairs. In smaller halls the 
type shown in Fig. 10-25f may be used, and for vestibules and narrow 
passages the same type in a size as small as 6 inches in diameter for a 40-watt 
incandescent lamp may be adequate. 

Light is essential in a closet unless it has less than 9 square feet floor area 
or is not more than 18 inches in depth, or where the light spilled from an 
adjacent room is sufficient. When closets are located in hallways it is often 
practical to place the hall fixture in front of the closet door. A simple 
porcelain pull-chain socket mounted just over the door frame on the 
opening side serves shallow closets. Deeper closets are better served by a 
small fixture, such as shown in Fig. 10-25f , mounted on the closet ceiling, 
controlled by a manual switch just inside the door or by an automatic door 
switch. A lamp rating of 60 watts is recommended as the minimum. 

Living Rooms 

In living-room lighting a degree of flexibility is desirable to meet varied 
requirements. This is provided by: 



INTERIOR LIGHTING 



10-37 




FIG. 10-26. Typical recommended living-room luminaires. a. Semi -indirect, 
ceiling-mounted (for incandescent-filament lamps), b. Semi -indirect, ceiling- 
mounted (for fluorescent lamps), c. Semi -indirect, suspended, d. Semi-indirect, 
multiple-arm. e. Wall urn. f. Decorative wall bracket, g. Recessed element, 
h. Window cornice, i. Side-wall valance. 

Ceiling fixtures. A ceiling center fixture similar to the types shown in 
Fig. 10-26 provides for the modest home (1) soft background lighting for 
more visually comfortable use of portable lamps, (2) lighting for game 
tables in center of the room without need to move portables, (3) convenient 
over-all room light upon entering, and (4) flexibility in the room's atmos- 
phere for varying occasions. The recommended types distribute light to 
the ceiling and side walls and diffuse light throughout the room. The re- 
commended minimums (14-inch diameter and 150-watt lamp) for the types 
shown in Figs. 10-26a and c will be adequate for rooms of 150 to 200 square 
feet or less. Large luminaires close to the ceiling are less consipcuous than 
small low mounted ones. Generally, they should be mounted not less than 
7 feet 6 inches above the floor. In small rooms with ceilings over 9 feet 
high, suspended types such as shown in Figs. 10-26c and d often are used. 



10-38 



I E S LIGHTING HANDBOOK 



Wall brackets and urns. Wall brackets and urns of either the purely 
decorative or functional type have living-room applications. The wall 
urn illustrated in Fig. 10-26e when used in pairs on opposite walls increases 
the general illumination of a room, especially in low-ceiling rooms and 
when located on the end walls of a long narrow room in which a centrally 
located luminaire lights side walls better than end walls. The type shown 
in Fig. 10-26f is better suited to purely decorative highlighting. In rooms 
of normal ceiling height they are mounted 5 feet 6 inches above the floor 
and should be arranged as part of a permanent furniture grouping. 

Built-in luminous elements. When cost is not a limiting factor, skillfully 
applied and balanced luminous elements (Figs. 10-26g, h, and i) offer 
endless possibilities and may replace the center fixture or augment it. 
The simplest methods are shown. An indirect, or luminous cove, con- 
tinuous or sectional, is not recommended for other than its decorative 
effect unless it can be mounted at least 1 foot from the ceiling. Greater 
separation and the use of directional reflectors is desirable. 

Table and floor lamps. To ensure desirable illumination levels for sewing, 
reading, and other seeing tasks, portable luminaires should be placed not 
more than 30 inches from the work unless a high level of general illumina- 
tion also is provided. Portable luminaires prove the most flexible means of 
obtaining light at desks, davenports, reading and sewing chairs, and pianos. 
(See Fig. 10-27.) Portable-lamp lighting proves more comfortable and 
less spotty when wall and floor brightnesses are sufficient to minimize con- 
trasts between the seeing task and the surround. 




FIG. 10-27. Typical wall, table, and floor lamps selected and placed for decora- 
tive harmony and to provide the recommended quantity and quality of illumina- 
tion. 



INTERIOR LIGHTING 



10-39 



Dining Rooms 

Whether the dining table is in a room of its own or is at one end of the 
living room or kitchen, it is the center of interest for that area. Linen, 
china, and polished silver can gleam only if the illumination is provided by 
large-area luminaires of proper brightness. The lighting method and the 
choice of luminaires, however, depend to a great degree on the activities at 
the dining-room table. If it serves as a dining area only, individual taste 
and a desire for sparkle may dictate. When the dining table is used also 
for sewing, studying, writing, or games, the recommended illumination for 
these tasks should be provided. The dining area, therefore, requires 
flexible lighting. It can be provided by a choice or combination of ceiling 
luminaire, brackets, and built-in lighting. (See Fig. 10-28.) 




FIG. 10-28. Typical recommended dining-room luminaires. a. Semi-indirect, 
with downlight. b. Semi-indirect, with inner diffusing bowl. c. Semi -indirect, 
multiple-arm. d. Shaded candles, e. Semi-indirect, for fluorescent lamps, 
f. Semi -in direct, ceiling mounted, g. Direct, spotlight or downlight. h. Over- 
cabinet lamp. i. Cove. 



10-40 I E S LIGHTING HANDBOOK 

Ceiling fixtures. When a luminaire is suspended over the table it 
becomes part of the table grouping and usually is mounted with the bottom 
of the fixture 30 to 36 inches above the table top. The types shown in 
Figs. 10-28a and d are designed so that a portion of the light emitted is 
directed downward to increase the brightness of the table and create sparkle 
by reflections from the silver, china, and crystal. When the dining table 
becomes a utility table after dinner, a luminaire should be chosen that 
produces lighting with the downward light diffused by means of a glass or 
plastic reflector, such as used in the type shown in Fig. 10-28b. 

When it is desired to mount a luminaire close to the ceiling rather than 
to suspend it, the types shown in Figs. 10-28e and f are recommended. 
The types shown in Figs. 10- 28a and c may be installed without suspen- 
sion. Close-to-ceiling luminaires, unless designed with a downlight com- 
ponent, will not highlight the table as the suspended type will. 

Wall brackets. Wall brackets add a pleasing note of decoration in the 
dining room and increase wall brightness. They usually are mounted 5 
feet 6 inches above the floor and should be used in pairs. They should be 
used in conjunction with a ceiling-mounted luminaire. Because of the 
remote location of wall brackets they alone cannot place dramatic emphasis 
on the table service. 

Built-in lighting. The dining room is adaptable to decorative lighting 
from window or wall valances, coves at opposite sides of the room, and 
recessed spots and lights in and above china cabinets. Coves and valances 
may provide general illumination. Valance and cornice lighting is appli- 
cable to the dining room also. Lamps may be installed on the top of high 
china cabinets to give additional background lighting as well as to be 
decorative. Downlights similar to that shown in Fig. 10-28g give dramatic 
emphasis to the table only. When downlights are installed over the table, 
additional luminaires, wall brackets, torcheres, urns, valances, or coves are 
necessary to reduce contrast and provide background lighting. 

Kitchen, Laundry, and Garage 

Illumination design for kitchens should provide (1) light distributed 
generally about the room, and (2) light specifically directed on work areas: 
sink, range, counters, and dining table, for example. Luminaires similar 
to those shown in Figs. 10-29a, b, and c will provide general illumination. 
Indirect luminaires should be mounted so as to permit a wide distribution 
of light. The bright lamp neck should be shielded from the field of view. 
General illumination alone will not prevent the annoyance and incon- 
venience of working in shadow at the sink, range, or other work area. 
The type of luminaire installed over the sink depends upon window and 
cabinet treatment. A small duplicate of the central luminaire often is 
used. Luminaires such as those in Figs. 10-29a and c with a 100-watt or a 
40-watt lamp also may be used over the sink. Downlights similar to that 



INTERIOR LIGHTING 



10-41 




FIG. 10-29. Typical recommended luminaires for kitchen, laundry, and garage. 
a. General diffuse enclosing globe, b. Indirect, c. Semidirect, louvered, for 
fluorescent lamps, d. Direct, for incandescent-filament lamps, e. Direct, for 
fluorescent lamps, f. Recessed element, g. Wall bracket, for fluorescent lamps. 
h. Wall bracket, for incandescent lamps. 



shown in Fig. 10— 29f may be recessed in a ceiling or in a furred-down section 
between cabinets over a sink. Opal -glass plates should be used with 
incandescent lamps, stippled or etched glass plates or louvers with fluore- 
scent lamps. Where sinks stand against unbroken wall surfaces or beneath 
double-sash windows, a bracket similar to that shown in Fig. 10-29g in the 
former case, or 10-29h in the latter, often is attached to the wall or to the 
center connecting window frame. Bracket types such as shown in Figs. 
10-29g and h are suitable also for use over ranges and work counters. 
They should be mounted approximately 56 to 58 inches above the floor for 
greatest visual comfort. 

When lights are not built into cabinets to illuminate the counter surface, 
brackets similar to Fig. 10-29g should be installed on the wall under the 
cabinets. 

Illumination designs for laundries should provide light on work areas 
such as wash tubs, ironing board, ironer, and counters or sorting table. 
A single ceiling luminaire cannot properly light all of these areas. A 
minimum of two is recommended. Luminaires similar to those in Figs. 10- 
29a, d, and e are recommended over laundry work areas and basement 
work benches. 

In the garage two luminaires of the type shown in Fig. 10-29d are 
recommended. 



10-42 



I E S LIGHTING HANDBOOK 



Bedrooms 

Bedrooms in the home are used for dressing, applying make-up, reading, 
sewing, and studying as well as for sleeping. A ceiling luminaire is recom- 
mended for every bedroom. The types in Figs. 10-30a, b, and g are similar 
in performance, and the choice between them depends on individual 
preference. The type shown in Fig. 10-30d may be preferable for child- 
ren's rooms, since it has very low brightness when viewed from reclining 
positions. The recommended minimums (14-inch diameter and 150-watt 
silvered-bowl lamp) are adequate only for small- and medium-sized rooms. 

For built-in dressing tables between wardrobes, excellent illumination 
for make-up is provided by a recessed luminous element in a furred-down 
ceiling. (See Fig. 10-30h.) Thin etched glass is recommended for fluores- 
cent lamp elements and diffusing opal for incandescent lamp designs. The 
dresser top should be mirrored to reflect light under the chin. 

Luminous panels on each side of the mirror are excellent when inset in the 
wall as in Fig. 10-30f. Lamps with half-cylinder shades (Fig. 10-30c) 
may be mounted on the mirror. A bracket with an open-bottom oval 
shade placed over the door mirror is inexpensive. 




FIG. 10-30. Typical recommended bedroom luminaires. a. Semi-indirect, 
for incandescent-filament lamps, b. Semi-indirect, multiple-arm. c. Bracket (fluor- 
escent lamp), d. Indirect, e. Bracket for door mirrors, f. Recessed elements for 
illumination at a mirror, g. Semi-indirect, for fluorescent lamps, h. Recessed 
fluorescent element, use over vanity. 



INTERIOR LIGHTING 



10-43 



Wherever fixed luminaires are not installed, portables are needed. Wall- 
mounted luminaires over the bed and tall bed-side table luminaires will 
provide illumination for reading. Portables at the dresser, desk, reading, 
or sewing chair are recommended. A small 6-watt night lamp plugged into 
a low convenience outlet is desirable, especially in nurseries. 

Bathrooms 

The most important illumination in the bathroom is that at the mirror. 
The face of the person in front of the mirror, not the mirror, should be 
illuminated. The ideal method is to provide a luminous area around the 
entire mirror circumference. Two brackets, one at each side of the mirror, 
mounted approximately 5 feet 6 inches above the floor, also provide good 
coverage. Either incandescent or fluorescent lamps may be used as in 
Figs. 10 31e and g. The length of the fluorescent tube distributes more 
light over the face and neck. Where the budget permits only one lighting 
outlet in the bathroom, a shaded-lamp over-mirror luminaire can be used, 
lamps are shaded. 

Unless a bathroom is less than 60 square feet in area, it should have a 
ceiling luminaire. If a small budget necessitates a choice between a ceiling 
luminaire and mirror illumination, the room should be illuminated from the 
mirror area. A wall switch inside the bathroom door should be used to 
control all luminaires. 

Enclosed showers should have a vapor-proof ceiling luminaire such as 
that shown in Fig. 10-3 Id, controlled by a switch outside the compartment. 
In large bathrooms a recessed element over the tub also is a convenience. 
It should be switch controlled at the door. 

For safety and convenience, a night light in the switch plate at the door 
or one in the baseboard is recommended. 







^ 





^ 


■ 






? 




K 


i 


' 








1 — n 






il 




j — 


f e 







g 






FIG. 10-31. Typical recommended bathroom^luminaires. a. General diffuse en- 
closing globe, b. Semidirect, ceiling-mounted, for incandescent-filament lamps, 
c. Semidirect, ceiling-mounted, for fluorescent lamps, d. Vapor-proof, for shower, 
e. Semi-indirect, bracket with lens. f. Semi -indirect, bracket, g. Wall bracket. 



10-44 



I E S LIGHTING HANDBOOK 



Floor, Table, and Wall Lamps 

It is possible, through skillfully planned built-in forms combining efficient 
fluorescent and spotlight sources, to develop satisfactory lighting throughout 
a home without the use of portable lamps. Such a plan requires relatively 
fixed positions for furniture, and its cost at present makes it impractical for 
the average home. Most homemakers still prefer the flexibility and 
decorative character of portable lamps. Fixed ceiling luminaires do not 
produce the illumination levels recommended for difficult seeing tasks at 
furniture groupings. Therefore, portables are recommended. 

Each portable, be it a table, floor, or wall type, should harmonize in 
scale, material, and form with its room environment and produce the level of 
illumination recommended in Table 10-7 for the seeing task associated with 
the specific grouping for which it is selected. (See Fig. 10-27.) Table 
10-8 gives the range of wattage ratings of incandescent and fluorescent 
lamps required to meet these footcandle recommendations. Table 10-8 
also gives efficient lamp heights and shade diameters for the desired 
distribution. 

Inner diffusing bowls. The I.E.S. certified lamps of 1933-1941 had 
diffusing bowls within the shades. The purpose of diffusing bowls is 
to improve the quality of lighting for the more exacting seeing tasks, to 
reduce the brightness of incandescent-lamp filaments rated 100 watts and 
greater, to soften shadows, and to minimize reflected glare. This im- 
provement in quality is gained with some loss in luminaire efficiency. 



Table 10-8. Recommended Characteristics of Portable Luminaires 
for Use in the Home 





TOTAL LAMP WATTS 


HEIGHT OVER- 
ALL 

(inches) 


SHADE 
DIAMETER, 




Incandescent 


Fluorescent* 


(inches) 


Lamps for flat-top desks 
and tables 


100-150 


30-40 


19-28f 


14-18 


Vanity lamps for: 
Dressing tables 
Dressers 


75-100 
75-100 


15-20J 

15-20 


20 
2(3 


S-lOf 
8-10t 


Wall lamps 


75-100 
100-150 


15-40$ 


50-60 
above floor 


8-10§ 

12-18|| 


Floor lamps 


150-500 


1f 


50-58**ft 


16-20$$ 



•Lamp watts only. Does not include power consumed by auxiliary and refers to straight tubes only. 

tSome models using fluorescent lamps may be shorter, since the long form and moderate brightness allow 
a lower position within the shade, with a wider resultant spread of light. 

tin vanity and wall lamps utilizing straight fluorescent tubes full-length shielding is required. 

§This size is appropriate only with 75- watt, incandescent-filament lamps (without diffusing bowls) over 
sinks and both sides of a dressing-table mirror. 

IIThis size (with bowls) required for critical seeing tasks, for use over beds desks, sewing machines, chairs, 
etc. 

1'Circular fluorescent lamps (32-watt) are being used as supplementary sources. 

**An adjustable feature is most desirable in floor lamps in order to fit the height to the varying seating 
heights of lounge chairs and davenports. 

ttTotally or semi-indirect torcheres should be 60 to 66 inches high. 

JJThe shades on small-scale bridge lamps may be smaller (10 to 14 inches), since the extension arm brings 
the source closer to the user. 



INTERIOR LIGHTING 10-45 

Shape, size, and density of bowl are important. For noncritical seeing 
tasks, table lamps 19 to 24 inches high equipped with two adjustable 
sockets for GO-watt incandescent lamps are satisfactory. Inner bowls 
should not be used in dressing-table lamps. 

Shades for portable luminaires. Shade linings should be white, ivory, or 
a very pale tint. Slant-sided shades aid in spreading light over a wider 
area. Shades for floor and table types which utilize fluorescent lamps 
can be reduced in depth, and may therefore have desirable large lower 
diameters without appearing too heavy and out of proportion in a small 
room. Open-top shades produce interesting highlights on pictures and 
walls and provide a more uniform distribution of light. A disk of shallow 
louvers or of silk or plastic attached to the upper ring is often necessary to 
shield the lamp's "mechanics" from the view of standing observers. The 
transmittance and reflectance of shade materials should be balanced with 
the brightness of the lamps used so that the luminaire will blend with the 
surround brightness. 

Placement of portable luminaires. All portables should be placed close 
to whatever is to be seen. Most of those centered on a large table serve 
only for decoration. The type (floor, table, or wall) selected for a given 
grouping should be the one which brings the light source nearest the user. 
Swivel and extension arms are advantageous, especially at large desks, 
sewing tables, and broad-armed chairs. 

Luminaires used for sewing, writing, or other handwork should be placed 
on the side opposite the hand used so that the hand will not cast its shadow 
over the work. Shadows are minimized by diffusing bowls or fluorescent 
lamps and when a fixed ceiling luminaire is used in conjunction with the 
portables. 

Floor lamps usually should be placed toward the rear of the chair or 
davenport for which they are selected, so that a seated person does not 
view the under part of the shade. Luminaires should not be placed directly 
in front or behind a person. Secretary and other tilt-top desks require a 
floor type — either the small-scale bridge or larger swivel types, depending 
on the desk size. 

Davenports placed flat against a wall with no tables to accomodate 
portables are served best by floor types of the shorter dimensions given. 
Swivel-arm, floor-type portables serve spinet and miniature pianos, though 
a taller floor type placed close to the keyboard is better for upright or 
grand pianos. 

Dressing-table luminaires should be placed about 30 inches apart. 
Shades should be near white and at face height. Wall luminaires mounted 
over beds should be not more than 26 inches above the mattress top. 

Torcheres do not give sufficient downlighting for critical seeing. They 
serve best for soft background lighting, especially in halls, dining rooms, 
and game rooms. 

A balanced arrangement of luminaires within a room usually is pleasing. 



10-46 



I E S LIGHTING HANDBOOK 



FARM LIGHTING 



Farm Exteriors 



Though it may be used less frequently than other entrances, the front 
door of the farm home should be lighted as it may be the guest entrance. 
The rear or side entrance is used regularly and often leads directly to an 
auxiliary farm building. A high level of illumination is recommended at 
doors. Individual reflectors, projector-type lamps, or floodlights provide 
suitable coverage for the large open areas between and around the buildings 
fenced off from the rest of the farm land. (See Fig. 10-32a.) Except in 
midsummer such lighting is needed in the regular work day, either morning 
or evening or both. Luminaires should be suspended from brackets on the 
side of the buildings, or on poles. In any event, they should be as high 
as possible in order to distribute light over a wide area and should be 
securely installed. Their exact number and location and the lamp used 
depend on the individual farm and the distances and areas involved. The 
illumination provided close to the buildings themselves should be sufficient 
for routine chores. The spaces between may be satisfactorily lighted if 
dependence on silhouette vision as in street lighting is planned. 

Farm Buildings 

Two types of incandescent-lamp reflectors are used most frequently for 
farm buildings — the standard-dome reflector and the shallow-dome reflector. 
The standard industrial dome affords a greater protection from glare. The 
shallow-dome reflector spreads light over a wider area. Other reflectors 
frequently used are the angle type and, for local lighting, the deep bowl. 
In all cases, reflectors should be durable, efficient, and easily cleaned. For 
this reason, porcelain-enameled steel or aluminum is recommended. 




FIG. 10-32. a. Farm-yard lighting, b. Small r. 
75-watt lamp in an industrial-type reflector. 



m in a milk house lighted by a 



INTERIOR LIGHTING 10-47 

Milk House 

The milk house requires illumination, since considerable work is per- 
formed there during the dark hours following the milking of the cows in the 
late afternoon and early morning, particularly during the winter months 
when the days are short. The various operations such as milk separation, 
cooling, bottling, etc., require maintenance of most sanitary and orderly 
conditions. Illumination assists in carrying out such a program. 

For most rooms, a symmetrical arrangement provides the best light 
distribution. (See Fig. 10-32b.) Under some conditions, the arrangement 
of milk-handling equipment calls for local or localized-general lighting. 
For general lighting, 100- to 150-watt, incandescent-filament lamps should 
be specified; for localized-general lighting, 60- or 75-watt, incandescent- 
filament lamps and for local lighting, 25- or 40- watt, incandescent-filament 
lamps. Direct type, corrosion resistant reflectors or enclosing globes are 
preferable for general lighting, while deep bowl reflectors are preferable for 
local lighting. Not less than 5 footcandles and preferably 10 should be 
provided for general work. Higher levels justified for special operations 
are being provided in some places by fluorescent-lamp equipment. 

Barns 

There are many types of barns; the most common are dairy, horse, cattle, 
sheep, hog, and general barns. Typical barn design seldom provides for 
much daylight, and much of the regular work in a barn is done during 
hours when there is little or no daylight available. Good electrical illumina- 
tion is necessary. The care of the stock, especially the sick and the young, 
is aided by proper lighting. 

The dairy bam should have better lighting than most types because of 
the particular need of cleanliness, an important factor in keeping the 
bacteria content of milk at a low point. Usually, dairy barns are arranged 
in a series of alleys, one set for feeding and the other set for milking and 
cleaning. This lends itself readily to the installation of luminaires spaced 
10 to 15 feet apart down the center of each alley. (See Fig. 10-33a.) 
For the care of young calves box stalls with 4-foot partitions usually are 
located at one end of the barn. Unless an alley light comes directly op- 
posite, a local light over each stall is desirable. Shallow-dome reflectors 
using 60- or 100-watt incandescent lamps and mounted close to the ceiling 
are recommended. If the ceiling is open, the bottom of the reflector should 
be even with the bottom of the joist. For individual stalls 40- or 60-watt, 
incandescent-filament lamps are used. 

The cattle barn is a closed area containing feed troughs. In general, a 
row of lamps in reflectors over the troughs will provide adequate light at 
the troughs and over the rest of the barn floor. In large barns, additional 
outlets are necessary, and, therefore, general lighting for the entire area is 
recommended. With 12- to 15-foot spacings, the 60-watt lamp is preferred, 



10-48 



I E S LIGHTING HANDBOOK 



® INCANDESCENT LAMP 
FLUORESCENT LAMPS : 
40 WATT ,=!=, 30 WATT 



P© PENDANT OUTLET 
So ONE-WAY SWITCH 
30 THREE-WAY SWITCH 




FIG. 10-33. Lighting layouts for various types of farm buildings, a. Gambrel- 
roof dairy barn. b. Horse barn. c. Poultry laying house. 

The horse barn normally is arranged in a series of feeding and cleaning 
alleys, similar to the dairy barn. The lighting layout should be similar to 
that for the dairy barn. Luminaire spacing in the cleaning alleys should be 
such that light is distributed into all stalls. (See Fig. 10-33b.) The 
partitions usually are solid, in contrast to the open stanchions of the dairy 
barn. As in the dairy barn, there are individual stalls at one end. 

The sheep barn may be open or closed. Open sheds are enclosed to a 
height only sufficient to prevent the sheep from getting out and to protect 
them from the wind. Closed sheds are of common barn construction. In 
wide sheds usually there are two rows of feed troughs with a center runway. 
Here, general lighting supplied by 60- watt incandescent lamps in reflectors 
mounted at the ceiling is recommended. In narrow sheds a row of similar 
units directly over, or not more than 4 feet behind, the single feed trough 
will be found satisfactory. 



INTERIOR LIGHTING 10-49 

The hog house, especially the large-size community type, is somewhat 
similar to the enclosed sheep barn. Similar illumination is recommended. 

The general barn areas usually are apportioned to each of the general 
farm activities. The lighting described under the specific types of barns 
should be applied to the individual portions. The haymow is located in 
the upper portion of most barns. With one 100- or 150-watt incandescent 
lamp for each mow, placed near the ceiling in shallow dome, angle, or RLM 
dome reflectors, barn work is facilitated. In some localities the regulations 
require the use of dust-tight equipment. Luminaires should distribute 
light over the driveway or floor space located below and between the mows. 

Poultry Houses 

The poultry house usually includes the hen house, the brooder house, and 
the feed room, all of which may or may not be under the same roof. Light 
is necessary for the proper care of the flock and the maintenance of the 
houses. 

The hen house usually is illuminated for increasing egg production by 
extending the daylight period during the short fall and winter days. 

For a 20-foot by 20-foot hen house two outlets should be provided, spaced 
at the ceiling 10 feet apart, and midway between the droppings board and 
the front of the hous?. (See Fig. 10-33c.) Shallow-dome reflectors 
should be used to provide the highest levels on feed hoppers, water pans, 
and scratching floor. Some light should be provided on the roosts also. 
Sufficient light usually is provided for morning or evening by tAvo 60-watt 
incandescent lamps. Two 25-watt lamps will be adequate for all-night 
lighting. For large rooms, approximately one half a watt per square foot 
should be provided. Where lights are used in the evening they should 
be dimmed as the end of the period approaches so that the hens can see to 
get on the roosts before the lights are turned off completely. The dimming 
may be accomplished by operating an auxiliary circuit of 10- or 15 watt 
lamps alone for a sufficient time to allow the hens to roost before turning it 
off, or by means of dimming equipment. Clock or manual control may be 
used for both systems. Some poultry raisers use electric lighting only in 
the morning hours, eliminating the necessity for dimming equipment or 
auxiliary circuits. 

The brooder house, in which chicks old enough to be transferred from the 
incubator are kept, usually can be lighted by one 40-watt incandescent 
lamp mounted close to the ceiling in the center of the room. Ultraviolet 
radiation frequently is used in both the brooder and hen house. (See page 
16-16.) 

The feed room usually will contain feed bins and auxiliary space for 
grinding, mixing, etc. Large storage spaces should be individually lighted 
by 40-watt incandescent lamps. Adequate general lighting usually can be 
provided by means of a centered RLM dome. The best arrangement is to 
have a luminaire opposite alternate bin partitions. 



10-50 I E S LIGHTING HANDBOOK 

Silo 

The silo holds preserved green feed for the stock. A silo is a cylindrical 
tank, usually 20 feet to 40 feet high, with an attached chute containing a 
ladder. A 100-watt incandescent lamp, mounted at the top of the chute, 
will supply illumination both in the silo and on the ladder. If mounted at 
the top of the chute, it should be tilted slightly toward the side of the silo 
so that it provides some light in the interior of the tank. 

Farm Shops 

Farms usually have a small workshop, a larger work shop for rough work 
on large machinery, and a machinery shed. The lighting of the small shop 
in which a work bench, forge, anvil, grindstone, and similar tools are 
located should follow industrial-lighting practice, with special care taken 
to see that individual machines located against the wall are supplied with 
light by local luminaires. The large shop and machinery shed should be 
lighted as storage spaces, unless the fanner performs difficult visual tasks 
in these rooms. 

OFFICE LIGHTING 

Seeing tasks in an office include the exacting ones of reading fine print, 
faint and blurred typing, and pencilled stenographic notes. Furthermore, 
many office workers use their eyes continuously throughout the working 
hours for these critical seeing tasks. Many factors in addition to the kind, 
arrangement, and number of light sources contribute to the seeing con- 
ditions. These include color and size of the paper used and the characters 
on it ; contrast between paper and characters ; and the reflectance and color 
of desk tops, office machines, furniture, walls, ceiling, and floor. 

Seeing conditions should be appropriate not only for workers having 
normal vision but also for those having defective vision. In many cases 
there is a possibility that the work or seeing task may be simplified. Type 
sizes encountered in offices range from 6-point to 12-point. The latter 
(larger size) is preferable. Paper of high reflectance and dull (mat) finish 
provides the best contrast with dark characters. The physical proportions 
of certain forms, ledgers, and books may affect the visual task; the use of 
ink rather than pencil for notes and order forms usually is helpful. The use 
of convenient furniture which permits and encourages good posture may 
simplify the lighting problem. One difficult seeing task results from the 
use of large numbers of carbon copies prepared from worn-out carbon 
paper on low-reflectance copy paper. 

Quantity of Illumination 

In general, the more exacting the visual task, the higher the quality 
and the quantity of illumination must be supplied for the same ease of 
seeing. The illumination levels provided for tasks such as encountered in 
drafting, designing, bookkeeping, and office-machine operation (i.e., long 
periods of work on fine detail) should be higher than those provided for 



INTERIOR LIGHTING 



10-51 



casual and intermittent efforts. Such considerations were recognized in 
the preparation of the recommendations in Table 10-9. The recom- 
mended illumination levels should be maintained as a minimum in service 
on the work or in the space in which the given activitj^ is carried on. 

Quality of Illumination — Brightness Levels 

Quantity and quality of illumination are related in offices as in all other 
areas. The standard of quality usually is higher in offices than in industrial 
applications, because of the relative ease of controlling office surrounds. 
Nevertheless, glare (both direct and reflected) is so commonplace that 
specific attention should be given it. Visibility usually can be improved 
by moving the light source from the line of vision, and by reducing its 



Table 10-9. Recommended Values of Illumination for Offices' 1 



CRITERIONS 



Difficult Seeing Tasks 
Involving: 

1. Discrimination of fine detail 

2. Poor contrast 

3. Long periods of time 
Such as encountered in: 

Auditing and accounting 
Business-machine operation 
Transcribing and tabulation 
Bookkeeping 
Drafting 
Designing 
Ordinary Seeing Tasks 
Involving: 

1. Discrimination of moderately fine detail 

2. Better than average contrast 

3. Intermittent periods of time 
Such as encountered in: 

General office work except for work coming under 
seeing tasks" above 

Private office work 

General correspondence 

Conference rooms 

File rooms 

Mail rooms 
Casual Seeing Tasks 
Such as encountered in: 

Washrooms, and other service areas 

Reception rooms 

Stairways 
Simple Seeing Tasks 
Such as encountered in: 

Hallways and corridors 

Passageways 



'Difficult 



FOOTCANDLES 

MAINTAINED IN 

SERVICE 



50 



30 



10 



'Recommended Practice of Office Lighting, Illuminating Engineering Society, New York. 



10-52 I E S LIGHTING HANDBOOK 

brightness toward the eye. However, since room proportions and other 
limitations occasionally do not permit this, the choice of the luminaire 
becomes of paramount importance. Large-area luminaires should be of 
lower brightness than small-area luminaires. Discomfort is influenced by 
factors which also effect a reduction in visibility. 

The quality of illumination in an interior depends on the brightness 
ratios in the field of view. It is recommended that the following maximums 
not be exceeded: 

MAXIMUM 
AREA RATIO 

Between task and surround 3 to 1 

Between task and remote surfaces 10 to 1 

Between luminaires (or windows) and adjacent surfaces 20 to 1 

Anywhere within the normal field of view 40 to 1 

The brightness of luminaires in offices should not exceed 400 foot- 
lamberts in the zone between 45° and 90° above nadir. 

Reflected glare frequently occurs because of the relative positions of 
windows or luminaires and of polished machine parts, specularly reflecting 
desk tops, and glossy paper. Glass desk tops, glossy papers, and glossy 
desk tops (especially dark ones) should be avoided. Even with such cau- 
tions the character of the task and surround may make some degree of 
specular reflection inevitable. Therefore, luminaire locations to the rear 
and to one side of the worker are to be preferred. 

Harsh shadows and alternate light and dark areas in strong contrast are 
undesirable because it is difficult for the eye to adapt itself almost simul- 
taneously to two brightness values in the same field. For this reason, 
local lighting, restricted to a small work area, is unsatisfactory. 

The larger and more widespread the area of the luminaire, the softer and 
less pronounced the shadows will be. Light-colored walls and ceilings 
having a mat surface diffuse the light by reflecting it in many directions, 
thus tending to illuminate areas in shadow. 

General Offices 

The nature of a general office presupposes a relatively large area. Eco- 
nomically, it is desirable to obtain maximum utilization of the available 
space, keeping in mind that, over a period of years, desks and partitions 
may be rearranged several times. In modern practice electric lighting is 
provided to make possible efficient arrangement of office equipment in- 
dependent of the available natural illumination. (See Fig. 10-34.) If 
practicable, the layout should be symmetrical, and, to minimize reflected 
glare, rows of luminaires should be run between desks rather than over 
them. The workers should face the least bright part of the luminaire. 
In most cases the end view of fluorescent-lamp luminaires presents the 
lowest brightness. 

In choosing the type of general-lighting system to be used, it is desirable 
to establish in advance a set of specifications and to use the design which 



INTERIOR LIGHTING 



10-53 



most nearly conforms to the specifications. The following specifications 
should be carefully considered and weighed as to their relative importance 
in the case under consideration: 

1. Standard practice: adequate illumination, proper protection against 
glare (both direct and reflected), proper distribution of light, and uni- 
formity of illumination. 

2. Efficiency of the system per unit of light emitted: this affects the 
operating cost and the heat load in the area. 

3. Maintenance: ease and expense of cleaning, service convenience. 

4. Sturdiness: long life, low service cost. 

5. Appearance: in conformance with occupancy and architectural design 
of the interior, lighted and unlighted. 

6. Flexibility: opportunity to increase light output at some future 
time, outlets so located that partition changes can be made without re- 
location of luminaires. 

7. Heat: temperatures and methods of disposing of excess heat. 
Supplementary lighting. For general office work, supplementary lighting 

on the desks usually is not desirable because of the difficulty of lighting a 
large enough area to include the entire working surface, and because of 
wiring difficulties. Local or supplementary lighting can be designed for 
business machines where the visual task usually is located on a sheet of 
paper or card fastened in some sort of holder or rack in a fixed position. 
Also, since the machines, as a rule, are electrically operated, power already 
is available at the desks or tables. 

In providing supplementary illumination for an area, it is important that 
adequate general lighting be provided also. Otherwise, there is likely to be 
too great a contrast between the relatively bright work and the dark 
surroundings into which the operator looks every time his eyes are raised. 
The ratio between task and surround brightness is important. For greatest 
comfort the brightnesses should be nearly equal. 





FIG. 10-34. Indirect luminaires with 500-watt incandescent lamps spaced on 10- 
foot centers provide an illumination of 25 footcandles of well-diffused light in this 
general office. 



10-54 



I E S LIGHTING HANDBOOK 



Private Offices 

Conditions in a private office vary in character but may be classified as 
follows: 

1. Occupant working alone or dictating to secretary. 

2. Occupant conferring with one or more visitors. 

3. Secretary working at a desk. 

In the first classification the seeing task may be severe. In most cases, 
however, it is intermittent in character. In the second classification the 
seeing problem is the examination of reports and records. In the third 
classification the seeing problem is similar to that of the general office, and 
the secretary's desk should be provided with the illumination recommended 
for the most severe task encountered. In meeting these conditions, two 
basic differences between general and private offices are recognized. The 
first is that in the private office there is far less latitude in furniture place- 
ment with reference to windows and walls (both possible sources of glare) 
than in the large general office. Second, the co-efficient of utilization is 
small for small rooms and, therefore, other things being equal the wiring 
capacity (watts per square foot) must be greater for equal illumination. 
Another difference is that private offices more frequently have glass 
partitions, glass-covered pictures, glossy furniture, and glass-covered desk 
tops. All are potential sources of reflected glare. 




FIG. 10-35. Private-office installations, 
a. U-shaped layout; b. L-shaped layout; c. 
open square. 



INTERIOR LIGHTING 10-55 

The luminaire design and layout is particularly important in private 
offices. The following plans have been found to have advantages when 
the luminaires have a considerable direct component. (See Fig. 10-35.) 

U-shaped layout. For the small narrow office in which the occupant 
often sits between a desk and table, luminaires can be arranged in a U- 
shape with the open part away from the window, and the closed (or cross 
piece) approximately over the occupant. 

L-shaped layout. For the small square office, with diagonal desk and 
table arrangement, the L-shaped layout can be used with the apex of the L 
approximately over the furniture in the corner and the legs of the L parallel 
to the walls. If possible the natural lighting should enter from the occu- 
pants' left (for right-handed persons). 

Open square. When several individual luminaires are to be used, their 
arrangement to form an open square may be advantageous as compared 
with spotting them at existing outlets. 

Supplementary center panel. To supplement a symmetrical layout, a 
large-area luminaire can be used if so arranged that it supplies direct 
illumination on the work area and maintains comfortable brightness ratios 
without introducing reflected glare. 

Conference Rooms 

Tt is common practice to provide more elaborate interior decoration in 
board of directors' and conference rooms than in outer offices, and the 
lighting in these rooms usually conforms to the architectural style of the 
interior. Not less than 30 footcandles should be provided over a conference 
table, and the illumination should be diffused to eliminate shadows on the 
faces of persons seated around the table. Undesirable reflections from the 
table surface should be avoided. (See Fig. 10-36.) High-reflectance mat 
surfaces are recommended. 

Reception Rooms 

For reception rooms, a general level of 10 footcandles should be provided. 
If the receptionist does stenographic and clerical work, the higher illumina- 
tion required should be provided by supplementary sources. Unless ample 
general illumination is furnished such equipment should be available for 
use also by persons who wish to read while waiting. (See Fig. 10-36.) 

Drafting Rooms 

Drafting makes very serious demands upon the eyes, since it involves 
accurate discrimination of fine details, frequently over long periods of time. 
A high level of glareless illumination should be provided. The contrast 
between the work and the background may be very poor, as, for example, 
when tracing a faint blueprint or a worn pencil drawing. Reflected glare 
from a specular drawing surface as well as from the polished T square, 
celluloid triangle, or scales may be particularly annoying and should be 
avoided. Care must also be taken to eliminate shadows along the drawing 



10-56 



I E S LIGHTING HANDBOOK 





FIG. 10-36. Attractive reception room and conference room. 

edge of the T square or triangle as well as multiple shadows from the 
drawing instruments or the draftsman's hands. On horizontal boards any 
ceiling or luminaire brightness may be reflected by the work to the eyes of 
the draftsman, and also the T squares, triangles, and curves may cast 
shadows. With the board in a vertical position, specular reflections cause 
little if any discomfort, and shadows are minimized. Furthermore, the 



INTERIOR LIGHTING 



10-57 




FIG. 10-37. Lines of luminaires are run diagonally across the ceiling of this draft- 
ing room to eliminate shadows at working edges of T squares and triangles under 
most circumstances. 

board may be high enough to shield the eyes of the draftsman from lumi- 
naire brightnesses otherwise in the field of view. Where boards are hori- 
zontal, straight edges of T squares parallel to line sources of illumination 
may cast sharp shadows unless the edges are leveled. To eliminate such 
shadows when the straight edge is parallel to the long side of the drafting 
table, it is recommended that this side be placed at an angle of 15 to 20 
degrees with the lines of lighting equipment (Fig. 10-37) . 

A drafting table with a frosted or white glass top illuminated from below 
to a brightness on the order of 300 footlamberts is recommended for use in 
tracing in rooms with 50 footcandles of general illumination. This is a 
method of solving a problem which is most difficult to accomplish by over- 
head lighting. It is desirable to keep the temperature of the tracing table 
as low as possible; therefore, light sources having a high lumen-per-watt 
rating should be selected. The desirable brightness of the glass depends 
on the nature of the work and the level of illumination from above. The 
draftsman should use opaque paper to cover the portion of the glass which 
is not concealed by the drawing in order to avoid the direct glare which 
would otherwise be experienced. 

Office Machines 

The seeing problems involved in the operation of business machines can 
be divided into three classifications: (1) locating keys, buttons, levers, and 
other controls on the machine itself; (2) reading printed, typed, or hand- 
written material from which the operator must operate the machine; 
(3) reading the results on the machine dials. 

Machine operation. The operation of most business machines does not 
present a difficult seeing problem and skilled operators do most of the work 
by the touch system. Letters or legends on the various keys are used as 
checks and during the training period. The general office lighting is 
adequate. 

Seeing the work. The copies of invoices, lists, etc., which the business- 
machine operator must transcribe accurately usually represent the most 



10-58 I E S LIGHTING HANDBOOK 

difficult seeing task in a modern office. The paper often is of poor quality 
and the characters nearly illegible, especially on sixth or seventh carbon 
copies, which are not uncommon. Contrast is likely to be very poor. 
Higher illumination is necessary if acceptable visibility is to be obtained. 
One hundred footcandles is recommended for this type of seeing task. 
In order to provide this illumination on the work the use of supplementary 
lighting is recommended. 

The luminaires should have low brightness so as to avoid specular re- 
flections. The light sources should be shielded from the direct view of the 
operator and others in the room. Where the operation requires rapid 
switching of visual attention between the machine and the work, it is 
desirable to have the brightness of the machine approximate that of the 
work. 

Reading results on dials. The reading of the dials of business machines 
may be difficult, particularly when the dials become worn. Often the best 
way to solve this problem is by building a light source into the structure of 
the machine. 

Machine finishes. Though most office machines such as typewriters, 
addressographs, billing machines, and so forth have some glossy external 
parts that reflect incident light in such a manner as to annoy an operator, 
some recent models may be obtained with a higher-reflectance mat finish 
than has previously been considered standard. Glaring reflections from 
flat specular surfaces can be overcome by proper orientation of the lumi- 
naires, but convex specular surfaces such as rods, buttons, and bands may 
cause trouble regardless of the luminaire orientation. Dark finishes have 
been almost universal, yet, between white papers in or about the machine 
and the dark machine surfaces, undesirable contrasts result that may be 
very fatiguing to an operator. Dark desk tops also can be a source of visual 
discomfort. It is recommended that all polished specular surfaces be 
eliminated from machines. It is recommended also that the machines 
themselves, as well as the desk tops on which they are installed, be finished 
in "light" colors (reflectance of the order of 30 to 35 per cent). 

Files 

General correspondence files often are arranged in a rectangle around a 
file clerk's sorting desk. This permits easy access to the files and allows a 
general overhead lighting system to illuminate the desk, the vertical faces 
of the files, and the opened drawers. The general lighting system should 
provide not less than 30 footcandles on the work plane. (See Fig. 10-38.) 
The seeing problem for ordinary correspondence and card files is concerned 
with inclined and vertical surfaces, and the seeing is by means of brightness 
and color contrasts. Though much file material is white, colored stock 
often is used. Such surfaces may be satisfactorily illuminated by a well- 
diffused, general-lighting system of the indirect or semi-indirect type, or by 
a direct large-area, low -brightness source. This type of illumination results 



INTERIOR LIGHTING 



10-59 




FIG. 10-38. An office, including files, business machines, typing, and work desks, 
lighted with plastic luminous-bowl indirect luminaires. 



in a minimum of shadow in a typical opened file folder; and the person ob- 
serving the files does not cast a sharp shadow over the work. In spaces 
where files are opened only occasionally and the room conditions do not 
permit well-diffused illumination, direct-lighting sources may be found 
satisfactory. Direct-lighting luminaires should be mounted above the 
aisle space between the files so that the downward light may penetrate the 
folders in the drawers. In some types of filing systems, a number of over- 
lapping cards in trays or drawers are held in position at the bottom edge by 
a specularly reflecting transparent material. The index and other printed 
or typed matter appear along the bottom line of the cards and are viewed 
through the transparent material. When illumination is provided by a 
general overhead system of direct or semidirect luminaires, one or more may 
be seen reflected specularly from the transparent material, making it 
difficult (frequently impossible) to read the printed matter. Because of 
the various angles at which the trays may be placed, it is difficult to position 
supplementary units at any point in the immediate areas above the files so 
as to avoid specular reflection. However, if by providing a fairly high 
level of illumination with indirect lighting, or large area sources having 
relatively low surface brightness, the brightness of the specular reflection 
from the surface of the transparent material may be reduced to little more 
than the brightness of the surface beneath, it will not interfere with one's 
vision. In many catalogue files, the catalogues are arranged vertically as 
are the books on book shelves. An illumination on vertical files of about 15 
footcandles usually will accompany a level of 25 to 30 footcandles on the 
horizontal. 



10-60 I E S LIGHTING HANDBOOK 

Service Areas 

Mail room. For the variety of seeing tasks encountered in a mail room, 
30 footcandles of uniformly distributed illumination is recommended. 

Corridors and passageways. Any passageways not separated from the 
working space by high partitions should have the same general illumina- 
tion as the rest of the office space. In corridors and passageways having 
high partitions, lower levels of illumination may be adequate. If the 
partitions are of glass so that the lighting equipment is visible from the 
rest of the office, the same restrictions with respect to brightness of the 
luminaires should be observed as in general office space. Outlets should 
be placed at locations such as corridor intersections, in front of elevator 
doors, and at the top and bottom of stairways. Luminaire spacing 
should not exceed about 1^ times the mounting height to achieve a 
reasonable degree of uniformity. 

Stairways. Luminaires in stairways should be located so that persons 
do not cast shadows of themselves over the stairs, so that stairway treads 
are not in shadow, and so that glare at eye level is avoided. In general, 
an overhead luminaire should be located at each landing. The arrange- 
ment should be such that adequate illumination will be provided after 
allowing for the failure of any one lamp. Recessed luminous elements in 
the walls near the floor often are advisable near landings and especially 
where one or two steps connect different elevations in corridors. A 
change in the color of the floor or baseboard at these locations also will 
assist in calling attention to the change in elevation of the floor level. 

Lavatories. In these areas a general lighting system which will provide 
not less than 10 footcandles is recommended. Mirror lighting is desirable 
in rest rooms and wash rooms. (See the discussion of bathroom lighting, 
page 10-43.) 

STORE LIGHTING 

No field of lighting presents as many or as diverse problems to the 
designer as that of lighting the modern store. No two stores are alike. 
They range in size from small one-man operated shops to large department 
stores with hundreds of employees. The merchandise displayed and sold 
in these areas varies in size from needles to automobiles, in texture from 
polished metalware to wool blankets, in reflectance from black worsteds 
to white sheets, and through all the colors of the rainbow. Some kinds of 
merchandise are transparent or translucent, others opaque. Vertical 
surfaces are the important ones to be appraised in some cases, in others it 
is the oblique, rounded, or horizontal surface that the customer inspects 
when buying. It is evident that the store-lighting designer must be 
versatile and able to apply all the lighting tools and techniques. 

To make its full contribution to successful, profitable merchandising, 
store lighting should be planned not only to provide favorable conditions 
for rapid and accurate evaluation of the inherent qualities of merchandise, 
but also to attract attention to the store, to dramatize the store and its 



INTERIOR LIGHTING 10-61 

specific features, and to make most effective all the other appointments of 
the establishment. In large proportion, the latter (architectural form, 
decoration, materials, fittings, layout) are designed to have the appealing 
appearance required by modern visual merchandising methods. When 
approached from this viewpoint, a store becomes a pattern of brightness 
and color varjdng in significant steps to attract attention, stimulate in- 
telligent buying and selling, and create a favorable, lasting impression. 

Store lighting should be planned with the following objectives in mind: 
controlling traffic; influencing circulation, speeding buying decisions and 
impulse purchases; increasing sales per customer per square foot per sales 
person; and increasing over-all profit. 

Representative of the illumination values which have been found effective 
in stores are the following, arranged in steps which are significant from the 
standpoint of attention value: 

Circulation areas • 20 footcandles 

Merchandising areas 50 

Show cases, wall cases, counter displays, etc. 100 

Featured displays in store and in window 200 

500 
1,000 

In some low-volume establishments in very light traffic areas somewhat 
lower values may suffice, whereas competitive conditions and the sales 
potential in other situations may dictate higher levels than those recom- 
mended. In any event, flexibility in the facilities provided, especially 
for accent lighting in store and window, adds greatly to the value of the 
system. 

Store Luminaires 

Store luminaires have a three-fold function: (1) to shield the customer's 
eyes from the brightness of lamps; (2) to direct light from a bare lamp from 
the angles where it is not wanted, or where it creates glare, to angles 
where it will contribute to the merchandise brightness and the interior 
brightness pattern; and (3) to enhance the decorative plan and to contribute 
to the architectural effects. 

Functions of Store Lighting 

Store lighting should (1) help attract attention to the store and its 
merchandise; (2) produce facilities for good seeing so that shoppers can 
judge the qualities of purchasable items accurately and quickly; and (3) 
create a store interior which is a pleasant and comfortable place in which 
to shop and sell. 

Store lighting design is not standardized. Although by chance many 
stores are lighted similarly — corner drug stores, for example — yet there 
is no incentive to attempt any such standardization because store owners 
seek to obtain individuality. Store lighting is, to a degree, allied with 
stage lighting in that both require good showmanship. 



10-62 



I E S LIGHTING HANDBOOK 



Attracting customer attention. Although some owners operate on the 
assumption that their store is a warehouse of merchandise to which people 
can come when they wish to purchase needed items, most stores feel the 
need for getting and holding customers' attention, and consequently 
employ such modern promotional methods for drawing shoppers to their 
stores as radio, printed advertising, posters and signs, and brightly lighted 
stores and show windows. The primary function of store lighting for both 
owners and shoppers is to draw attention to items of merchandise. By 
lighting cases and other displays the merchandise brightness can be in- 
creased to give the articles display value. (See Fig. 10-39.) 




FIG. 10-39. Good store lighting increases merchandise brightness and background 
contrasts and thus attracts customer attention to items on display. 



Evaluating mechandisc . Store lighting should create a favorable seeing 
condition at the point-of-purchase by which a shopper can quickly and 
accurately appraise the inherent qualities, color, texture, form, and Avork- 
manship of merchandise. Lighting for this purpose can be extended also 
to setting up lighting conditions such as those that exist at the seashore, 
or in a ballroom, so that customers can accurately appraise the merchan- 
dise as it will be seen at the point of use. (See Fig. 10-40.) 

The problems of lighting for attractive display, and lighting for correct 
appraisal, overlap for many articles that are handled as both display and 
stock items. Normally such items are displayed in show cases, wall cases, 
on shelves, and in garment cases, but can -be removed for closer inspection 
and purchase. Since the merchandise will be seen in both locations — 
display and purchase point — it is evident that the lighting for these two 



INTERIOR LIGHTING 



10-63 







FIG. 10-40. Lighting aids in establishing an atmosphere conducive to accurate 
appraisal of merchandise with respect to its ultimate appearance in use, indoors 
or out. 

locations should be so related as to color, level, and quality that it will 
suffer no change in appearance when moved from one point to the other. 

Lighting for the quick and accurate appraisal of merchandise is of 
first importance to shoppers, but is of benefit to the store owner also. It 
speeds the selling function and helps to reduce the number of items re- 
turned for credit because of their changed appearance when seen under 
the lighting at the point of use. 

Store appearance. In order that their stores may impress shoppers 
favorably and thereby induce them to linger, buy, and return, store owners 
strive to create an atmosphere which is consistent with the kind of mer- 
chandise sold and acceptable to the store's clientele. For example, the 
kind of surroundings desired in an infants' wear shop is different from that 
needed in a hardware store. 

The picture-impression of a store is the summation of all of the visible 
elements (arrangement, furniture-, displays, lighting, etc.) but some ele- 
ments weigh more in this picture-impression than others. It is believed 
that the brightness pattern is the dominant element in this picture. 
(See Fig. 10-41). 

Factors That Influence Seeing and Buying 

Although shoppers may use all of their senses in appraising merchandise, 
the sense of seeing is undoubtedly important. The tone of a piano is 
important, but so is the kind of wood in the case and its finish; the frag- 
rance of perfume seems more alluring when the container is attractive also ; 
the materials, workmanship, and styling of shoes, as much as their fit, 
is reflected in their price; salads are selected by cafeteria patrons by 
their appearance. 

Time. The human eye requires time to see. All other factors being 
equal, objects illuminated to higher footcandle values with resulting higher 
brightnesses can be seen in less time than those of lesser brightness. 

Size. Large objects, and large details of pattern and texture, are easier 
seen than small ones. Appraisal often requires the study of small details of 



10-64 



I E S LIGHTING HANDBOOK 




FIG. 10-41. A lighting installation contributes to the over-all appearance of a 
store and should be planned with the character of the merchandise and clientele in 
mind. 

workmanship, label copy in small type, or intricate pattern details; higher 
illumination values have the effect of making them easier to see. This is of 
particular value to older persons and others who have subnormal vision. 

Contrast. A high contrast between an object and its background is of 
value in attracting attention to displays. Dark objects displayed against 
light backgrounds are noticed more quickly than those viewed against 



INTERIOR LIGHTING 10-65 

dark ones, and vice versa. A displayman needs a versatile array of lighting 
equipment (background lights, spotlights, floodlights, color filters, etc.) to 
create these contrasts. Each display should be considered a miniature 
stage setting designed to draw attention to a specific area, and to make the 
merchandise shown there attractive to shoppers. Contrast can be ob- 
tained by brightness and color differences between objects and their 
surrounds. 

Brightness. The end product of illumination and reflectance is bright- 
ness, which attracts attention and aids in seeing. 

Reflectance. The reflectance of a wall, ceiling, or merchandise surface 
indicates the proportion of incident light that will be reflected. Reflec- 
tance therefore controls brightness. It is important to know the character 
of the reflection as well as its value. For example, a white tablecloth, a 
white china plate, and a polished silver cream pitcher may have the same 
reflectance (80 per cent). The cloth, however, reflects its light diffusely 
and looks equally bright seen from any angle; the china plate looks white 
also, but its glazed surface adds specular reflections; the polished silver 
cream pitcher looks dark except for the reflected highlights of light sources 
and bright surrounding. 

In order that unwanted and uncontrolled reflections in wall and ceiling 
areas may be avoided, surfaces that have diffusing, or near-diffusing, char- 
acteristics are recommended. These characteristics are typical of mat and 
eggshell finish paints, wallpapers, woods, etc. 

The use of color. Accurate merchandise appraisal depends in part upon 
the color quality of the lighting. A fluorescent lamp may produce a day- 
light quality light and an incandescent-filament lamp a reddish yellow light. 
Each affects the apparent color of merchandise. Lighting that fails to 
show merchandise as it will appear under the lighting where it mil be used 
often is responsible for a customer's dissatisfaction and return of the goods. 
Returns may be as much as one-eighth of gross sales in some stores. 

In addition to affecting the apparent color of merchandise, the color 
quality of illumination has an important bearing on the atmosphere and 
the decoration of a store. The complexions of customers and salespeople 
are affected also. This is especially important in fitting rooms for men's 
and women's wearing apparel. If the lighting does not complement the 
complexion, it will affect adversely the approval of the fitting. It is 
recommended that light of a "warm" color be provided to enhance facial 
appearance. 

Design Factors in Store Lighting 

Most stores need a good balance of horizontal and vertical illumination. 
Luminaires having a light distribution normally used for general lighting 
purposes usually will produce not more than half as much illumination on 
vertical as on horizontal surfaces. (See Fig. 10-42.) While common 
interior lighting layout procedures are designed to provide uniform illumi- 
nation on a horizontal plane, many objects (wallpaper, draperies, tapestries, 



10-66 



I E S LIGHTING HANDBOOK 



; . -■■■ •" ■ :,'. 



■:.■./-.;::,.'■.-;.■' 




: "-' 3 



4111 •; 





FIG. 10-42. In many stores, light on vertical surfaces is at least equal in import- 
ance to that provided on horizontal surfaces. 

paintings, clothing, etc.) arc displayed and appraised vertically. Also, 
shelves at the perimeter of many stores are important display areas. These 
may be lighted by asymmetric distribution equipment supplementing 
general lighting. If luminaires that have strong horizontal components 
are selected for general lighting, it should be recognized that they may be 
uncomfortably bright also. There is less danger of this in small areas 
with luminaires high enough above the floor to be out of the customer field 
of view. 

Luminaire briglttness and contrast with ceiling. Whether lumin; - es are 
glaring or not depends upon their brightness relative to that their 
surround. Luminaire brightness may be reduced by shielding or by 
concealing the equipment from the normal field of view . (See Fig. 10-43.) 

Highlights. Highlights are useful in revealing the form of semispecular 
objects such as silks, leathers, glassware, pottery, etc. Highlights created 



INTERIOR LIGHTING 



10-67 








FIG. 10-43. To minimize glare from luminaires, they should conceal the lamps 
from view. The luminaire brightness should be not much greater than that of its 
background. High reflectance ceilings and upper wall surfaces and some indirect light 
component aid in reducing contrasts. 

by concentrated incandescent-filament sources are essential for displays of 
diamonds, jewelry, etc. Large-area, low-brightness highlights are more 
suitable for automobiles, furniture, and similar objects. (See Fig. 10-44.) 

Sliadoivs. Downlighting creates shadows that are sharp and dramatic. 
Indirect lighting and large-area diffusing sources produce soft shadows that 
tend to flatten the appearance of rounded objects and conceal surface 
textures. Shadows help to reveal the form of objects and texture of ma- 
terials. (See Fig. 10-45.) They should not be so dense that they conceal 
merchandise on shelves or in cases. Sharp shadows on customers' and 
clerks' faces usualby are not flattering. 

Maintenance. Proper maintenance of a lighting system pays dividends. 
The amount of light absorbed in dust and dirt on transmitting and re- 
flecting surfaces may equal that which reaches the merchandise. Regular 
maintenance is made inexpensive when lighting equipment is easy to clean 
and lamp changes are easy to make. Group replacement of all lamps at 
some predetermined point in their life may be the most satisfactory pro- 
cedure. (See pages 6-2 and 10-20.) 

General Lighting of Stores 

Genera 'ighting is necessary in every store. For certain kinds of stores 
and typ A merchandise, uniform general lighting providing the recom- 
mended : i'v. /el of illumination is by itself satisfactory. Food markets, 
variety sto.es, and others that display items primarily on open, closely 
spaced tables and counters are in this category. (See Fig. 10-46.) Usually, 
few display cases are used and perimeter shelves are considered principally 
as stock rather than display areas. 



1068 



I E S LIGHTING HANDBOOK 




] r 



- 






■■■. 




FIG. 10-44. Highlights assist in displaying specular and semi-specular surfaces 
and refractive materials to best advantage. Point sources are required to make gems 
and glassware sparkle. Large areas of brightness add the sheen to glossy surfaced 
merchandise. 

Interior-Display Lighting for Stores 

Stock merchandise located and arranged for display is a large and im- 
portant portion of display in the average store. 

The ratio of illumination on the merchandise in its display position to 
that at its final appraisal point should be planned for maximum display 
value and minimum appearance change. Usually, if the ratio of illumina- 
tion inside the case to that outside is approximately 2 to 1, the merchandise 
will have adequate display value without suffering in appearance when re- 
moved for appraisal. An illumination level inside glass-enclosed cases 
twice that incident on glass sides and top compensates for surface reflections 
that reduce the visibility of the merchandise. In order that customers may 
see through these surface reflections, the brightness inside must be higher 
than that of the surface reflections. Internal illumination is particularly 
necessary in glass-enclosed wall cases because, unless luminaires are located 
close to perimeter walls or supplementary units are provided, the general 
illumination level usually is lower at the room perimeter than at the center. 



INTERIOR LIGHTING 



10-69 





FIG. 10-45. Shadows produced by carefully controlled beams of light can create 
dramatic effects, bring out flowing lines, and reveal the texture of mat-surfaced 
materials. 



Mirror^s. Since shoppers commonly use mirrors to appraise articles of 
clothing in which they are interested, accent lighting at mirrors is im- 
portant. The place where the shopper stands or sits, rather than the mir- 
ror, should be illuminated. A mirror may he used as a reflector to light 
the lower part of the figure. Three things are important: the face should 
be illuminated with diffused light of a color that flatters the complexion; 
the sales item should be adequately lighted over its entire surface; the 
quality of light should be planned to display best the type of materials 
most often sold in the area. 

Vertical displays. Clothing, floor and wall coverings, and tapestries and 
draperies often are hung vertically for display and appraisal. Uniform 
illumination from top to bottom is desirable. (See Fig. 10-42.) 

Column displays. The utilization of columns (especially the large col- 
umns found in many old buildings) as display centers not only helps to 
conceal the columns but adds appreciably to the display footage. (See 
Fig. 10-47a.) Such display destroys over-all supervisory visibility also, 
and therefore may not be acceptable in all cases. Troughs, built-in lumi- 
nous elements, and remote spotlights are effective. 



10-70 



I E S LIGHTING HANDBOOK 




FIG. 10-46. In stores that display items on open, closely-spaced tables general 
lighting often is used alone. 




FIG. 10-47. a. Column displays, b. Display niches, c. Canopied displays. 



INTERIOR LIGHTING 



10-71 



Niches. In departments where stock is concealed and merchandise is 
small in size, display niches can be effective. These niches usually are 
lighted by built-in equipment. (See Fig. 10-47b.) 

Canopies. A canopy is an effective * 

device for attracting attention to a 
display grouping or for emphasis of ,_- 

certain merchandise. (See Fig. 10 - 
47c.) It also may divert attention 
from a bad ceiling conditon. Cano- 
pies form useful ledges behind which 
tubular indirect lighting may be con- 
cealed. Further, they can serve to . 
lower portions of ceilings to con- 
ceal more efficient (shorter projection 
distance) downlighting. 

Platform and dais displays. The 
preferred mood to be created by an 
open platform or dais display is free- 
dom and spaciousness. (See Fig. 10 - 
48.) Light from a remote location, 
e.g., a near-by column or the ceiling, 
is desirable. The light may be trained 
and controlled by means of spot re- 
flectors, reflector lamps, or floodlights. 

Counter displays. Overcounter 
lighting may provide background ac- 
cent, silhouetting, or direct illumi- 
nation, depending on the merchan- FIG. 10-4S. Platform and dais dis- 
dise and effect desired. P la ys often are lighted by remotely lo- 

cated projectors. 





Directional signs. Since the colors of illumination that may be applied 
in most displays are limited, color stimulation often is used in directional 
signs as well as in wall decoration, upholstery, etc. Many opportunities 
exist for carrying advertising or directional messages on walls, canopies, 
column displays, etc. (See Fig. 10-49.) 

Window Lighting for Stores 

Show windows fronting on a high-density pedestrian traffic-way are one 
effective medium for informing the public of items for sale and of inviting 
them into a store. They are the physical bond between the street and 
pedestrian-way and the store interior, and they can be made a stage on 
which a merchant's goods are dramatized. (See Fig. 10-50.) Show- 
window lighting should be versatile, often almost as flexible as stage light- 
ing, and it should supply brightness, which attracts attention and minimizes 
veiling glare. Many modern windows are decorated as a foreground for a 
view of the store interior. This is called open-front design. 



1072 



I E S LIGHTING HANDBOOK 




FIG. 10-49. Directional, departmental, and advertising signs. 

General lighting. High-level general illumination usually is the first 
requirement in show windows. However, in large prestige-type stores 
dramatic accents sometimes are considered more important. Often a 
window is illuminated to compete at night with other neighborhood light- 
ing, or to display merchandise successfully under adverse daytime condi- 
tions created by window-glass reflections of sky brightness or other 
daylighted areas. 

Accent lighting. Emphasis or accent lighting is provided by individual 
spotlights which sometimes are used with dramatic effect, even without 
general diffuse lighting. 

Supplementary lighting. In certain types of windows, footlights are 
desirable because of the difficulty of projecting light to the face or the 
merchandise (which the pedestrian sees) from luminaires located directly 
above. Footlights are effective also when a geometrical disposition of the 
glass to eliminate reflections caused by daylight-created brightness is 
desirable, and overhead lighting is difficult to use effectively without creat- 
ing reflected glare. 

Because a show window has the prominence of a stage and compares with 
it as a center of attraction, lighting equipment should be located carefully 
so as not to create glare. A luminaire should not attract attention to 
itself. The common concealment techniques (valances, flush and recessed 
mounting, and louvers) provide satisfactory results when planned for all 
angles of viewing. Normally, there is no need to protect from glare at the 
back of the window. 

Open fronts. With open-front windows in particular, and with other 
types also, the window orientation with respect to sunlight and skylight is 



INTERIOR LIGHTING 



10-73 




FIG. 10-50. Closed- and open-back store windows and a typical open-front store. 



10-74 



I E S LIGHTING HANDBOOK 



being given increased study. From a practical standpoint, it is impossible 
at present to build up the illumination level in a window sufficient to over- 
come completely the veiling glare produced by bright sky reflections, sunlit 
light-colored buildings, and other adverse conditions. Studies have indi- 
cated that when the average reflected brightness is twice the brightness 
behind the window glass, the reflection is at the threshhold of producing 
deleterious veiling glare. Many architectural methods have been devel- 
oped for the practical solution of this problem. These include sloping 
windows, which reflect lower brightness areas such as those of which the 
brightness can be controlled by awnings, marquees, or canopies. (See 
Fig. 10-51.) 




FIG. 10-51. By proper orientation and shading of glass surfaces, the brightness 
of reflected images in the pedestrian field of view may be reduced below that which 
interferes with viewing the window display. 

SCHOOL LIGHTING 

The trend in education toward greater dependence on visual techniques 
emphasizes the importance of lighting in schools. Illumination aids mate- 
rially in the accomplishment of the visual tasks encountered by students 
and teachers and, in so doing, is beneficial in preserving good vision, aiding 
impaired vision, minimizing visual strain and fatigue, and increasing the 
over-all efficiency of the educational process. 

Also, it is recognized that the provision of a model environment for 
health and happy living and work at the formative stage in a child's de- 
velopment is one of the contributions which classroom experiences can 
make to his general education. By using the techniques available today, 
light sources, equipment, materials, and proper natural and electric il- 
lumination in combination with high-reflectance room and furniture finishes 
can provide attractively colorful and cheerful, yet comfortable and efficient, 
seeing conditions for students and teachers. 

Despite the existence of these techniques and the availability of the 
equipment and materials required to put them into practice, many schools 
make poor use of natural illumination and have no provision for electric 
lighting. 

School routine has much to do with this indifference toward lighting. 
Ordinarily, the hours that a classroom is used each day are few, and inten- 
tionally most school buildings are constructed, located, and oriented to 
make available as much daylight as possible. However, it is only within 



INTERIOR LIGHTING 10-75 

recent years that the close relationship among interior decoration, seating 
plans, and utilization of daylight has been recognized. 

Electric illumination is required during the winter and on cloudy and 
stormy days to compensate for reduced daylight levels and, because of 
crowded conditions in many urban areas, to make possible staggered and 
evening sessions. 

Classroom Characteristics 

The commonly accepted area unit of school lighting is the classroom 
with provisions for seating twenty to forty pupils at individual desks. 
Certain features of such typical classrooms are of special interest with 
respect to lighting. 

Sealing. Most classrooms arc designed for distributed seating, making 
it advisable to plan the lighting for uniform results throughout the entire 
room. In older schools seats invariably are arranged so that all pupils 
face in one direction. While this still is a dominant plan, there are a con- 
siderable number of exceptions, especially in the lower grades. Here 
groupings of six to twelve around individual tables is an accepted practice. 

Daylighting. The greatest number of classrooms are arranged with 
large windows dominating an entire wall to the left of the pupils as they face 
the front of the room. This window space has a strong influence on bright- 
ness ratios, since it is seldom that daylight is absent during regular school 
hours. 

Sight-saving classrooms. One of the most serious problems in school 
lighting arises in connection with pupils whose eyesight is so defective as 
to justify special consideration. It is standard practice in some school 
systems to place such pupils in special classes under expert care. Special 
sight-saving classrooms are provided in which these students perform their 
difficult visual tasks. Since their eyes are unable to function normally, the 
best possible conditions should be provided such pupils to compensate for 
their impaired vision. (See Fig. 10-52.) 

Surround. Because many critical visual tasks are encountered, class- 
room brightness ratios should approach unity. (See Table 10-11.) Light 
distribution from windows and luminaires should be planned in combina- 
tion with room and furniture surface finishes with this in mind. It is par- 
ticularly important to have high-reflectance ceilings (80-85%), walls 
(50-60%), desk tops (35-50%), floors (15-30%), and chalkboards. 

Chalkboards occupy a large portion of the surround, often covering 
most of three walls. They are located at a critical glare angle (0 to 20 
degrees above the horizontal line of sight) and frequently at present they 
are of dark gray slate or other low-reflectance material. (See Fig. 10-53.) 

For effective classroom operation the visibility of material on chalk- 
boards, particularly on those at the front of the room, should be good. 
Almost always supplementary lighting is desirable because of the poor 
legibility of many types of handwriting and the difficulty of maintaining 
good contrast between the chalk and the board, 



10-76 



I E S LIGHTING HANDBOOK 



~L 




FIG. 10-52. A sight-saving classroom. 

Table 10-10. Recommended Illumination Levels for Classrooms and 

Other School Areas 



AREA 



Classrooms, including study halls, libraries, shops, lecture 
rooms, laboratories, etc 

Sight-saving classrooms, drafting rooms, and sewing rooms 

Gymnasiums and swimming pools 

Auditoriums, cafeterias, and similar rooms not used for study.. 

Reception rooms, locker rooms, washrooms, stairways, and cor- 
ridors containing lockers 

Corridors and storerooms 



FOOTCANDLES 
MAINTAINED 
IN SERVICE 



30 
50 
20 
10 

10 
5 



Table 10-11. Recommended Brightness-Ratio Range Limits for 
Classrooms and Other School Areas 



AREAS 



Task and immediate background such as desk top, wall, 
etc 

Task and more remote parts of room 

Light source (luminaire or sky) and adjacent ceiling or 
wall 

In no case should the ratio be combined to suggest the 
acceptability of a range greater than 



RECOMMENDED BRIGHT- 
NESS RATIO RANGE 
LIMITS IN NORMAL 
FIELD OF VIEW 



1 to 3— 3 to 1 

1 to 10—10 to 1 
1 to 20—20 to 1 
1 to 30—30 to 1 



INTERIOR LIGHTING 



10-77 




FIG. 10-53. Typical chalkboard installations in classrooms: standard slate (left) ; 
high-reflectance (right). 

Equipment for the illumination of chalkboards should be located above 
and in front of the top edge of the boards in such a manner that specular 
reflections from the boards will not strike pupils' eyes. The most satis- 
factory location for equipment with a high degree of control is at the ceiling, 
mounted at a horizontal distance approximately three-quarters of the 
vertical distance from the center of the board to the ceiling. Equipment 
of the diffusing type may be mounted much closer to the board, but also 
preferably at the ceiling. 

Maintenance of Classroom Lighting 

Classroom design and decoration should be planned for maintenance 
simplicity as well as for good initial characteristics. In particular, pro- 
vision should be made for regular cleaning of lamps, luminaires, and room 
surfaces in order to maintain the highest possible illumination level. 

Because adequate maintenance schedules have not yet been generally 
adopted in schools, a low maintenance factor should be used in design cal- 
culations, unless it is known that a regular schedule will be adhered to. 

Design Standards 

There is considerable standardization in classroom size, room height, 
seating arrangement, hours of occupancy per pupil, visual tasks, and sur- 
roundings. Illumination and brightness recommendations given in Tables 
10-10, 10-11, and 10-13 are universally applicable. Higher levels would 
provide better conditions but are not at this time considered to be economi- 
cally feasible for the average installation. 

The ratios given in Table 10-11 can be maintained by many types of 
equipment and with many spacing arrangements. The average classroom 
is 20 to 26 feet wide and 26 to 35 feet long, with a 10- to 12-foot ceiling. 
Two rows of three overhead luminaires is the most common arrangement. 
Continuous rows of surface or suspension-mounted, fluorescent-lamp lumi- 
naires have met with approval. In most cases these should be arranged 
parallel to the line of sight. Table 10-12 and Fig. 10-54 describe the most 
common layouts. 



10-78 



I E S LIGHTING HANDBOOK 



To maintain brightness ratios within the recommended range with 
incandescent lamps, it is usually necessary to use indirect or semi-indirect 
luminaires. The brightness of the luminous indirect type often may be 
made to match that of the ceiling, but the coefficient of utilization of the 
semi-indirect type usually is greater. Fluorescent lamps permit the use 
of a semidirect fixture type as well as of a semi-indirect type; troff'ers 
and other direct-lighting luminaires can meet the 20-to-l brightness ratio 
standard only when wall, ceiling, floor, and furniture surfaces are of high 
reflectance and are well maintained. The brightness limits shown in 
Table 10-13 should be used as a guide in the choice of luminaires. 



Table 10-12. Maintained Average Illumination Level Provided by a 

Variety of Installations in a Typical 23 by 32-Foot Classroom 

Laid Out as Shown in Fig. 10-54* 



TYPE OF 


LAMP DATAf 


LUMI- 
NAIRE 
EFFI- 
CIEN- 
CY 


WATTS 
PER 

SQ FT|| 


FOOT- 
CANDLE 
RANGE If 

33-41 


ROOM 
PLAN 


LIGHTING 


No. 
6 


Watts and Bulb 


Lamp 
Lumens 


Type J 


(Fig. 
10-54) 


Opaque or lumi- 


1,000, PS-52 


21 , 500 


I 


70-80 


8.2 


la 


nous Indirect 


6 


750, PS-52 


15,500 


I 


70-80 


6.1 


24-30 


lb 


90%-100% up 


8 


750, PS-52 


15,500 


I 


70-80 


8.2 


32-40 


2a 


10%-0% down 


12 


500, PS-40 


9,950 


I 


70-80 


8.2 


31-39 


3 a 




56 


40, T-12 


2,100 


F 


70-S0 


3.6 


30-38 


4a 




30 


100, T-17 


4,000 


F 


70-80 


4.7 


31-39 


5a 




84 


40, T-12 


2,100 


F 


70-80 


5.5 


45-56 


5b 




40 


100, T-17 


4,000 


F 


70-80 


6.3 


41-51 


6a 


Semi-indirect 


12 


500, PS-40 


9,950 


I 


70-80 


8.2 


34-49 


3a 


60%-90% up 


56 


40, T-12 


2,100 


F 


70-80 


3.6 


33-48 


4a 


40%-10% down 


30 


100, T-17 


4,000 


F 


70-80 


4.7 


34-49 


5a 


General 


48 


40, T-12 


2,100 


F 


65-75 


3.1 


33-43 


4b 


Diffusing 


42 


40, T-12 


2,100 


F 


65-75 


2.7 


29-38 


5c 


40%-60% up 


72 


40, T-12 


2,100 


F 


65-75 


4.7 


50-66 


5d 


60%-40% down 


48 


40, T-17 


2,100 


F 


65-75 


3.5 


33-43 


6b 


Semidirect 


42 


40, T-12 


2,100 


F 


60-70 


2.7 


31-43 


5c 


10%-40% up 


48 


40, T-17 


2,100 


F 


60-70 


3.5 


35-48 


6b 


90%-60% down 


60 


40, T-12 


2,100 


F 


60-70 


3.9 


44-61 


7a 


Direct 


60 


40, T-12 


2,100 


F 


60-70 


3.9 


52-64 


7a 


0%-10% up 


40 


40, T-12 


2,100 


F 


60-70 


2.6 


35-43 


8a 


100%-90% down 


64 


40, T-17 


2,100 


F 


60-70 


4.7 


55-68 


8b 



* Recommended Practice of School Lighting, Illuminating Engineering Society, New York. 

t Other types or sizes of lamps in similar equipment may be used, the footcandle result being proportional 
to the total lumens of the lamps. 

t I = Incandescent. F = Fluorescent. 

§ Assumed over-all efficiency of the luminaire in per cent. 

|| Including watts consumed by control equipment with fluorescent lamps. 

' The footcandle value within this range will vary, depending on the efficiency of the luminaire within the 
amounts indicated for that characteristic and on the light distribution within the range described for the type 
of lighting. Illumination values also will be different for other maintenance factors, room sizes, ceiling 
heights, ceiling reflectances, and wall reflectances. Values used are: maintenance factor = 70 per cent; ceiling 
height = 12 feet; ceiling reflectance = 75 per cent; wall reflectance = 40 per cent. 



INTERIOR LIGHTING 



10-7!) 



2a 



— ©-}— © © — 

j 12 FT j 

-»f-eFT*- 




4a 
4b 



5a 
5b 
5C 

5d 



7F 



ffe 



6a 

6b 



6 FT 

— i— 



7a 



H 



■ff- -ff" 



8a 
8b 



mil if 


mini 



FIG 10-54. Typical general lighting layouts for a 23-foot by 32-foot classroom. 
Detailed data on applicable lamps and luminaires and on related illumination levels 
are given in Table 10-12. 

Lecture Rooms 

Two levels of illumination are quite desirable in lecture rooms, provided 
supplementary illumination is provided for the lecture table or teacher's 
rostrum. This permits the use of contrast when attention to the speaker 
or his demonstrations is of primary importance, and a high level of general 
lighting for quizzes and taking notes. 

Libraries and Reading Rooms 

Local lighting often is used in these rooms, especially when the student 
is seated along long tables for reading. Assuming recommended levels of 
illumination are provided, and proper brightness ratio maintained, either 
localized-general or general lighting may be satisfactory. (See Fig. 10-55.) 



Table 10-13. Recommended Maximum Zonal Brightness Limits for 
Classroom Luminaires 



ZONE 


MAXIMUM BRIGHTNESS LIMITS* 


Vertical to 45 degrees 

45 to 60 degrees 

60 degrees to horizontal 


1,000 footlamberts 
450 
225 



* If the area involved is small, brightness values up to twice those shown may be acceptable when all in- 
terior surfaces have a high reflectance mat finish. 



10-80 



I E S LIGHTING HANDBOOK 



Those who advocate the localized-general combination feel that it is more 
economical (assuming large areas devoted to bookcases and racks), that it is 
helpful ps3 r chologically because of the tendency to concentrate attention, 
and that it provides the simplest way of providing the recommended light- 
ing levels. Advocates of general lighting point out that general lighting 
is usually cheaper to install, and that any type of local lighting subject to 
individual control may work against the desires or comfort of an adjacent 
student. 

Wall cases or stacks should be illuminated separately, preferably with a 
luminaire designed to distribute light adequately both vertically and 
laterally. 

Drafting Rooms (See Office Lighting page 10-55.) 

Art Rooms 

The recommended general illumination level may be supplemented by 
means of lighting equipment such as spotlights or projector lamps designed 
and installed to increase the visibility of models and other such material 
from the back of the room. Many instructors prefer electric lighting for 
this purpose because its color and the shadoAvs it casts are the same through- 
out the day. Since north skylight is preferred, electrical illumination 
should blend well with it. Daylight incandescent and fluorescent lamps 
frequently are used. 

Sewing Rooms 

Sewing room practices vary appreciably in different school systems, and 
it is difficult to establish uniform standards for all. Because of the common 
use of dark materials, and the minute size of the detail to be seen, very high 
illumination levels are recommended. These can best be provided by 
installing luminaires to supplement the general lighting. Each machine 
and work table should be furnished with supplementary lighting. 





EMBhHS 

FIG. 10-55. Typical school library and reading room. 



INTERIOR LIGHTING 



10-81 



Laboratories and Shops 

The work shops of the average school system are in most cases designed 
to simulate industrial shops. Therefore, it is recommended that the 
lighting of all such rooms follow industrial practice. (See Fig. 10-56 
and the discussion of Industrial Lighting, page 10-94.) 




FIG. 10-56. Industrial type, fluorescent-lamp luminaires installed in a school 
chemistry laboratory. 

Cafeterias and Restaurants 

The highest illumination levels in cafeterias and restaurants should be 
found in the kitchen, at the serving counters, and at the cashier's desk. In 
the eating area the illumination should assist in creating a cheerful, com- 
fortable atmosphere. A relatively low illumination suffices if the rooms 
are used only for eating, since no difficult visual tasks are involved. If 
the rooms are used also as study halls, it is recommended that the luminaire 
and the layout be planned for two levels, one for eating and the other for 
study. 

Auditoriums 

School-auditorium lighting should be flexible. Often the room is used 
both as an auditorium and as a study hall. A level of at least 10 footcandles 
is recommended for assembly purposes and the classroom level of 30 foot- 
candles for lecture and Study periods. 

Corridors, Stairways, and Locker Rooms 

The recommended illumination level is 10 footcandles. Where locker 
installations are fixed, luminaires should be located so as to illuminate the 
face and interiors of lockers. Frequently a corridor-lighting installation 
does not adequately light stair landings, in which case additional luminaires 
should be installed for each landing. Care should be taken in locating 
stairway luminaires so that they illuminate the edges and faces of all steps. 



10-82 



I E S LIGHTING HANDBOOK 




FIG. 10-57. A dormitory room lighted for study hour. 

Dormitory Rooms 

Except in special schools (as in military schools, perhaps) there should be 
few differences between the lighting goals for dormitories and those for 
similar rooms in the home (bedrooms and living rooms). (See pages 10-36 
and 10-42.) Most of the differences are associated with lack of decoration, 
uniformity, ease of cleaning, and similar factors — few of which deal directly 
with the quantity and finality of illumination. (See Fig. 10-57.) Military 
dormitories may tend more toward general illumination from ceiling 
fixtures rather than localized illumination from portable lamps. Under 
such conditions, general-office lighting standards should be followed. (See 
page 10-52.) 

The lighting of dormitory rooms should satisfy two dissimilar require- 
ments : 

1. Contribute to a comfortable and attractive relaxation atmosphere. 

2. Provide the 30-footcandle classroom illumination level recommended 
for study purposes. 

Portable lamps at each desk and lounge chair maj^ be adequate if they 
distribute enough light throughout a room to bring brightness ratios within 
the classroom limits. 

COMMERCIAL AND PUBLIC BUILDINGS 

Almost any structure except a residence might fall into the category, 
"commercial and public buildings," but the term usually is construed by 
illuminating engineers to mean theaters, banks, libraries, and museums, 
and the public portions of office buildings, hotels, churches, concert halls, 
hospitals, and similar large areas of high turnover and intermittent oc- 
cupancy. Modern lighting design is co-ordinated with the architectural 
theme in public buildings more often than in other structures. The char- 
acteristic public-occupancy areas of such buildings include lobbies, audi- 
toriums, w r ork and service areas, corridors, stairways, and so forth. 



INTERIOR LIGHTING 



10-83 



Office Buildings 

The lobby of an office building usually is at street level. The simplest 
type is a wide hallway giving access to the elevators or stair wells. More 
elaborate lobbies may be used as an exhibit hall by groups occupying the 
building. Many have shops located along the sides. (See Fig. 10-58.) 

From a visual standpoint, decorative lighting that produces 10 footcan- 
dles in a lobby usually may be considered sufficient for safe passage of 
pedestrians, provided there is auxiliary lighting at directory boards, and 
directional signs, and adjacent to the elevators and stair wells as a safety 
measure. However, since most office buildings have their maximum traffic 
in the daytime, 5 footcandles may be found insufficient to provide satis- 




FIG. 10-58. Illumination in public-building lobbies. 



10-84 I E S LIGHTING HANDBOOK 

factory visual adaptation as the visitor steps into the lobby from out- 
of-doors (from an illumination level approaching 10,000 footcandles in 
direct sunlight). This necessity for adaptation combined with the ad- 
vertising value of higher levels and brighter surroundings has led many, 
building designers to provide higher levels of illumination (20 footcandles) . 

In hallways and corridors of ordinary ceiling height (less than 30 feet) 
luminaires should be spaced not more than 20 feet apart. No branch 
corridor should be without a luminaire. A luminaire located at a main 
corridor junction will serve two branches not more than 10 feet deep. For 
safety in such locations, at least two lamps should be used in each luminaire. 

No entrance to an elevator or a stair well should be more than 10 feet 
from a luminaire. The recommended average illumination level for 
elevators, and stair wells, is 10 footcandles, assuming high-reflectance sur- 
faces. The lumieaire and layout should provide such a uniform level that 
the maximum value at any place in the room is not greater than three times 
the minimum. 

Theaters 

Theater-lighting design begins outdoors with the combination decorative 
facade with display cases which identifies the entrance. Part of this en- 
trance is the marquee. Sources in the marquee often provide a high il- 
lumination level around the box office. This level is reduced along the 
traffic lane into the threater so that the theatergoer's eyes may become 
adapted gradually to the lower levels inside. 

Theater lobbies are passageways between the street and the foyer. An 
illumination level of 20 footcandles is desirable in lobbies. The walls and 
ceilings should have a high brightness (up to 50 f ootlamberts) . At signs 
announcing current or coming attractions 20 to 40 footcandles should be 
provided by local lighting for accent. The luminaires may be ceiling- 
mounted spotlights, or lamps and reflectors attached to the signboard. 

Foyers are areas where traffic is distributed into the auditorium. An 
illumination level of 10 footcandles is recommended. This is sufficient 
for recognition of acquaintances, for safe movement, and to arouse interest 
in the decoration, and yet permits quick adaptation to the lower audi- 
torium level. In larger theaters, a lounge or promenade may separate 
the lobby and the foyer. The illumination level in such an area should 
fall between those of the lobby and the foyer. 

In the auditorium proper, three rules should be observed: (1) bright- 
nesses should be low; (2) sources should be placed out of the normal field 
of view from any seat in the house; (3) in motion-picture theaters the 
light should be so controlled that a minimum falls upon the screen. (See 
Fig. 10-59.) Stray light reduces contrasts in the screen image. Brightness 
up to 10 footlamberts may be used between the acts. Luminaires should 
be located as far outside the field of view as practicable. See also Sec- 
tion 14. 

To relieve brightness contrasts between the screen and its immediate 
surround and thus contribute to eye comfort, a low brightness of approxi- 



INTERIOR LIGHTING 



10-85 




FIG. 10-59. A community theater auditorium. 

mately 1 footlambert on the surfaces adjacent to the screen is recommended. 
In lighting such surfaces, the source must be concealed and so directed that 
no light spills on the screen to reduce picture clarity. Any luminaire type 
may be used (coves, shielded downlights, or masked projectors) that will 
border the picture screen with surfaces of about one-tenth screen brightness. 

For motion-picture theaters, illumination levels can be graded from \ 
footcandle at the rear of the auditorium to y^ footcandle at the front. 
Some provision should be made to supply higher levels for emergencies, 
for cleaning, and at the end of the final presentation. 

Few theaters have sufficient illumination for program reading. In 
community theaters where the auditorium may be used for other than 
motion-picture projection additional lighting may be necessary. Theaters 
used solely for stage plays need not have over- all low-intensity lighting. 
A minimum of 5 footcandles should be provided everywhere for the read- 
ing of programs during intermissions. Individually controlled local lumi- 
naires on the backs of seats have been used successfully in some theaters 
to provide light for reading programs and for locating lost objects. 

Aisle lights located under the outside row of seats can provide useful 
illumination without introducing high brightnesses in the field of view of 
the seated audience. 

Some use is made of carpets impregnated with fluorescent materials 
which become luminous when irradiated by means of ultraviolet sources. 

Theater Stages 

The stage provides the most interesting lighting problem in the theater. 
Even those theaters designed exclusively for motion pictures occasionally 
may accommodate stage shows for charity, for community rallies, and 
so forth. , 

Stage lighting equipment includes border lights, footlights, spotlights, 
floodlights, and cyclorama floodlights. (See Fig. 10-60.) 



10-86 



I E S LIGHTING HANDBOOK 




FIG. 10-60. Typical plan and elevation for a large stage. 



INTERIOR LIGHTING 



10-87 




FIG. 10-61. Stage-lighting equipment; a. border lights; b. footlights; c. spotlights 
and flood lights. 

Border lights provide general illumination for the stage. Depending 
on stage depth, one to four rows are hung parallel to the curtain, with the 
first border as close behind the curtain as feasible. All border lights are 
mounted so that they may be adjusted vertically, since otherwise they 
might interfere with the use or placement of various stage sets, or not be in 
a position to supply the proper light distribution. Border lights include 
bare lamps in long troughs, individual lamps and reflectors grouped to- 
gether as troughs, and individual, separately operated spotlights. (See 
Fig. 10-61a.) In any case color flexibility is a requirement. Bare lamps 
with different filter coatings; individual reflectors with glass roundels or 
gelatin filters; and spotlights with gelatin filters are the primary color 
mediums. Usually three to five colors are used. All those of one color 
are wired for simultaneous control. They should be so spaced that uni- 
form coverage may be provided with any combination. Borders are elec- 
trically controlled so that each circuit may be dimmed. The incandescent 
lamps used include 40- to 60- watt bare lamps on 5- or 6-inch centers, 100- 
to 200- watt lamps in individual reflectors on 9- to 12-inch centers, and 250- 
to 500-watt lamps in spotlights. 

Footlights are located in front of the curtain line and usually consist 
of one row of sectionalized disappearing units. (See Fig. 10-61b.) Their 
purpose is to soften and eliminate harsh shadows which tend to appear on 
faces lighted only from above, and to provide illumination when the stage 
action requires the actors to move "downstage" near and beyond the 
curtain line. Like border lights, they may be bare lamps in troughs or in 
individual reflectors. Usually they are wired in several circuits, and are 
dimmer controlled, 



10-88 I E S LIGHTING HANDBOOK 

Spotlights and floodlights located in the wings adjacent to the border 
lights or in the auditorium proper provide accent lighting. (See Fig. 
10-61c.) Many stage designers use spotlights almost exclusively to pro- 
duce the required high levels, using border lights and footlights to provide 
a more uniform level than may be obtained with the imperfect spotlight 
overlap. A spotlight is a luminaire in which a reflector behind the lamp 
or sometimes a lens in front of it, or both, is used to focus the output of 
the lamp in a narrow beam. Incandescent lamps with ratings between 250 
and 2,000 watts and carbon arcs are used in spotlights. By comparison, 
floodlights have a wide beam. Lamps of any type and size are used, de- 
pending on the equipment size, with the control depending on a reflector 
behind the lamp and on the housing edge. 

Theater Lighting-Control Systems 

Theater-lighting circuits for both the stage and the auditorium often 
are equipped with dimming devices. The lighting should be expressive 
and versatile, achieved through dimmer blending of various color circuits 
and by regulating the quantity of light delivered to a particular area. 
When this blending or regulation is to be achieved as a part of the lighting 
sequence, the gradations of light should be produced smoothl}' and ac- 
curately. 

Dimmer control of auditorium lights facilitiates eye-accommodation. 
Even relatively low auditorium levels may cause momentary blinding glare 
when the lights are switched on immediately after either a dark stage setting 
or a motion picture has been viewed. 

Most dimmers regulate light output by varying lamp current. Indi- 
vidual preheat-starting (hot) cathode fluorescent lamps cannot be dimmed 
conveniently in this manner over a wide brightness range, since the arc 
extinguishes with a small voltage drop. However, the output of incandes- 
cent lamps and instant-starting cylindrical (cold) cathode lamps may be 
controlled smoothly over a very wide range. The most common dimmer is 
the resistance type. When not loaded beyond their rated capacity, re- 
sistance dimmers can handle smoothly the circuit to be controlled and 
dissipate the heat produced by its operation. Circular dimmers are de- 
signed for loads as high as 4,000 watts. When resistance dimmers have too 
little load for their rated capacity, complete blackout of the circuit is not 
possible. This condition is corrected by the addition of dummy loads or 
by the use of other types of dimmers, particularly variable autotransformer 
dimmers or electronic tube-reactor dimmers. 

Churches 

Lighting for churches should be co-ordinated with the church service, 
and suited to the architectural design. (See Fig. 10-62.) Soft well- 
diffused illumination is recommended. High levels attract the attention 
of the worshipper to the altar or pulpit at certain points in the sendees. 
The amount of illumination provided at the pews should be keyed to the 
amount of reading expected of the congregation, some of whom may have 



INTERIOR LIGHTING 



10-89 




FIG. 10-62. Typical church -lighting installations. 

impaired vision. If the illumination requirements vary during the service, 
provision should be made for switching or dimming as required. 

Church tradition and architecture are appreciably older than electrical 
lighting. Therefore, where a traditional plan is desired, electrical illumina- 
tion should supplement the natural illumination unobtrusively. 



10-90 



I E S LIGHTING HANDBOOK 




FIG. 10-63. Illumination of typical altars. 

For example, the Gothic church with high vaulted ceilings has depended 
in the past upon directional daylighting from great windows along the 
walls. The resulting shadows and dimly lighted vaults are responsible 
for the majestic beauty of the Gothic style. Therefore, artificial lighting 
for Gothic structures can be supplied best by luminaires of the direct type, 
supplemented if necessary by indirect and local lighting to minimize con- 
trasts or provide illumination levels suitable for reading. 

Other types of interiors call for a completely indirect lighting system. 
Concealed flush downlighting has been used successfully also. 

Directional spotlights, recessed-lens-controlled luminaires, pinhole down- 
lights, or coves and troughs may be concealed from view in a variety 
of ways. 

Indirect lighting which more readily results in diffuse and soft lighting 
is used in many churches of the congregational auditorium type, and in 
many with Greek or Roman temple plans. 

The altar sanctuary requires local lighting. (See Fig. 10-63.) Emphasis 
lighting can be directed to any area or object by equipment concealed in 
niches or behind ceiling beams. Glare protection for the congregation 
results from the angle at which the light is directed. Local lighting on 
pulpits and lecterns is almost always necessary. Conversely, general 
rather than local lighting, is recommended for the choir loft because of the 
difficulty of locating and adjusting local luminaires, and the possibility 
of resultant glare for the congregation. 

Banks 

Most banks have a main floor area, divided between the public portion 
and the service cages. For the public portions, many types of equipment 
are in common use. (See Fig. 10-64.) Sufficient illumination should be 
provided for the depositors' transactions. 

When the architectural style makes it difficult to provide adequate gen- 
eral illumination, local lighting at writing tables and on the tellers' side of 
the tellers' cages also is recommended, since critical seeing tasks are per- 
formed at these places and a low level of illumination may result in errors. 
Care should be taken to maintain low brightness ratios by means of high- 
reflectance surfaces and low-brightness luminaires. 



INTERIOR LIGHTING 10-91 




FIG. 10-64. Views of good lighting installations for banks. 

Museums and Art Galleries 

Museums and art galleries are primarily places for objects to be dis- 
played for study and appreciation. The illumination on vertical and 
oblique planes may be of greater importance than that on the horizontal. 

Color, line, proportion, and perspective, all of which are affected by light, 
are particularly important in displays. Well-planned illumination is 
based on a consideration of the artists' mediums, techniques, and objectives. 

General design guidance is provided in Table 10-14. It is doubtful if 
an art gallery can be designed to give satisfactory natural lighting during 
much of the year and the future may see such structures designed for elec- 
trical illumination only. 

Hospitals 

An operating room presents the most difficult lighting problem in a hos- 
pital. Illumination in excess of 1,000 footcandles is desirable on the operat- 
ing table; color is important; shadows and glare must be minimized; there 
should be no appreciable addition of heat at or around the operating table. 

A variety of installation plans have been developed. Recessed ceiling 
reflectors, controlled by prismatic glass plates, may be arranged in a rec- 
tangular or circular pattern around the table. With such an arrangement, 
doctors and nurses are not likely to obscure the light to an extent that will 
, handicap the operating surgeon. Suspended clusters of luminaires direct- 
ing light at the table from many angles provide similar diffusion. Another 
common method is to suspend over the table a large area reflector that con- 
trols the light from a single lamp. Beam spread can be varied by focusing. 
Flexible mounting permits aiming of the beam. (See Fig. 10-65.) Re- 
gardless of the plan or luminaire selected, the over-all room brightness 
pattern is important. A surgeon concentrates on a relatively small area 
but at times his visual field will include parts of the room. Therefore, 
the brightness of all areas in the room should be maintained uniform by 
high-reflectance surfaces and general illumination. The brightness should 
approach as closely as possible that at the operating table. 



10-92 



I E S LIGHTING HANDBOOK 



Table 10-14. 



Lighting Design Guide for Art Gallery and Museum 
Displays 









ILLUMI- 










NATION 




TYPE 


MATERIAL 


PRINCIPAL 

PLANE AND 

SURFACE 


LEVEL 
ON PRIN- 
CIPAL 
PLANE 

(foot- 
candles) 


REMARKS 


Cil paintings* 


Canvas 


Vertical 


30 


Annoying reflected 


Individual 


Wood 


Dull 


50 


images are likely to 


or group 


Silk 




30 


be formed of high- 


Unframed 


Velvet 




50-100 


brightness, poorly 
placed luminaires 


Framed 


Canvas 


" 


30 




Unframed 


Wood 


Vertical 


50 


To avoid reflections 






Glossy 


should net be dis- 










played on opposing 










walls 


Single 


Canvas 


Vertical 


30-50 


Mask completely from 






Glossy 


other objects; light 










as individual piece 


Water Colors* 










Group 




Vertical 






Framed and 




Gloss}' 


20 




Unframed 




Dull 






Murals* 


Plaster 


Vertical 




Display to avoid re- 


Individual 




Horizontal 


20-50 


flections 


Unframed 




Dull 








Glossy 






Etchings, en- 


Paper 


Vertical 




Display to avoid re- 


gravings, 




Dull 


20-30 


flections 


mezzotints* 




Glossy 






Group 










Framed 










Unframed 










Ceramics t 


China, etc. 


Inclined 




Generally shown in 


Group 




Dull 


20 


illuminated display 






Glossy 


cases 






Semiglossy 






Sculptures f 


Marble 


Vertical 


30-100 


See paper by H. L. 


Free-standing 


Terra-cotta 


Dull 


30-50 


Logan, "Modeling 


Individual 


Plaster 


Glossy 


30-100 


with Light," 




Wood 


Semiglossy 


20-100 


Ilium. Eng., Febru- 




Light bronze 




200 


ary 1941 




Dark bronze 




500 






Red copper 




300 






Green copper 




500 






Brass 




200 






Gold 




100 






Silver 




100 






Ivory 




30-50 






Wax 




30-50 





• Single plane involved. 



t Three dimensions involved. 



INTERIOR LIGHTING 



10-93 



The desired color usually is obtained 
by means of glass filters; other glass 
niters are used to absorb heat. It is 
preferable to provide operating rooms 
with a separate emergency lighting 
system or to have facilities to operate 
the regular system from an indepen- 
dent power supply in emergencies. 

Wards and private rooms have one 
problem in common usually not found 
in home bedrooms; most patients lie 
awake for long periods facing the ceil- 
ing. Both direct-lighting and high- 
brightness patterns from indirect lumi- 
naires should be avoided. The best 
type of luminaire is that with a wide 
upward distribution. It should not 
be mounted too close to the ceiling 
and should have a brightness in the 
patient's field of view approximately 
equal to that of the ceiling. Special 
wall-mounted types with a downward 
component for reading are available. 




FIG. 10-65. A hospital operating 
room showing the operating table 
luminaire and the small spot on which 
its beam mav be focused. 



Hotels 

There is no hotel lighting problem 
not covered by recommendations for 
other public buildings and for the home. 

For the guest rooms one point deserves special emphasis — the universal 
nature of the room. Often it is living room, bedroom, library, and dining 
room combined and sometimes a merchandising area as well. Therefore, 
a flexible lighting plan is recommended. General lighting may be pro- 
vided by a single central luminaire to be controlled by a switch near the 
entrance. Local lighting should be added for atmosphere and to provide 
adequate illumination for individual tasks (reading, writing, etc.). 

Hotel bathrooms require at least as much attention as a similar room in a 
home; the unfamiliar surroundings increase the importance of good lighting 
for shaving. (See page 10-43.) 

Hotel auditoriums differ in two respects from other auditoriums: 

1. They have flat floors so that they may be converted into ballrooms. 

2. Though a stage often is located at one end this may not be the focal 
point of attention. 

A symmetrical decorative and flexible lighting layout is recommended. 

Hotel lobbies are reception halls and are used as lounge rooms as well. 
Adequate illumination should_be provided for those who wish to read and 
write. Usually, portable lamps are practical. They emphasize the home- 



10-94 



I E S LIGHTING HANDBOOK 



like character of the hotel and are flexible and easily coordinated with any 
decorative scheme. 

INDUSTRIAL LIGHTING 

In 1915 the Illuminating Engineering Society prepared and issued a 
Code of Lighting Factories, Mills and Other Work Places. According to the 
procedure of the American Standards Association, revisions of the Code 
were made in 1921 and in 1930. The 1942 American Recommended Practice 
of Industrial Lighting, which is condensed here, is a development of the 
earlier codes. 

Illumination is an environment factor that affects every industrial es- 
tablishment. The advantages of good illumination to employees and man- 
agement are many. 

Production and Quality Control 

Under good illumination it is possible to see an object of much smaller 
size than is discernible under poor illumination. Continuous quality 
control throughout the manufacturing process, made possible by good 
illumination, permits early discovery and rejection of defective parts prior 
to further processing or final inspection. 

Floor space utilization. A uniform level of general lighting such as 
shown in Fig. 10-66 makes possible the most efficient arrangement of 
machinery and conveyors and better utilization of floor space. Manu- 
facturers have learned that in many cases more work can be achieved with 
less floor space when the work flows in straight lines through assembly or 
inspection sections. Good general lighting facilitates the arrangement of 
straight .production lines. 




FIG. 10-66. A uniform level of general lighting permits the optimum utilization 
of floor space and increases the flexibility of the production line plan in this shop. 



INTERIOR LIGHTING 



10-95 



Cleanliness. Industry has found that cleanliness pays. Poor illumina- 
tion makes it difficult to see into corners or under machinery and these dark 
areas collect dirt and waste that would otherwise be cleaned out. Where 
dirt can be seen it is more likely to be removed. In a well-lighted plant 
dingy areas do not exist and much more sanitary conditions prevail. 

Light and safety. Engineering for safe plant operation consists es- 
sentially of preparing a safe working environment. The environment 
should be designed to match and to compensate for the limitations of human 
capability. However, as revealed by an analysis of accidents and their 
causes, this is but one phase of the safety problem. Most personal injury 
accidents involve a combination of personal and mechanical causes. The 
chain of circumstances or series of causes which has led a workman to a 
potential injury frequently can be broken only if be can see quickly and 
accurately the causes and act to prevent the accident. 



Factors of Good Illumination 

There are many factors involved in good illumination. These can be 
summed up under the headings quality, which includes the direction and 
diffusion of light, its color, etc., and quantity. Separately and in conjunc- 
tion they have significant effects on the ability to see easily, accurately, 
and quickly. 

Quality of illumination: light diffusion and distribution. Some directional 
and shadow effects are desirable in general illumination for accentuating 
the depth and form of solid objects, but harsh shadows should be avoided. 
(See Fig. 10-67.) Shadows are sof- 
ter and less pronounced when many 
wide-distribution diffusing lumi- 
naires are used. Alternate light 
and dark areas in strong contrast 
are not desirable because the adapta- 
tion of an observer's eye to first 
one and then the other of the two 
brightnesses is fatiguing. For this 
reason, purely local lighting re- 
stricted to a small work area is 
unsatisfactory; there should be suf- 
ficient general illumination through- 
out the room. High (30 to 60 per 
cent) reflectance surfaces serve 
several purposes. They reflect light 
toward the working areas, they 
reduce contrasts between walls, 
ceilings, windows, and luminaires. 
Machinery with a high-reflectance FIG. 10-67. Uncontrolled shadows 

finish reflects light to otherwise sha- usually interfere with vision. How- 

, , ever, in some cases shadows may be 

dowed areas. utilized also to simplify seeing tasks. 




10-96 



I E S LIGHTING HANDBOOK 



Clearly defined shadows, without excessive contrast, simplify the seeing 
task in certain types of operations such as engraving on polished surfaces, 
scribing on metal, and some textile inspection. (See Fig. 10-67.) Con- 
trolled shadows may be provided b^y supplementary luminaires. 

Many of the seeing tasks in industry are on vertical or nearly vertical 
surfaces. Hence the amount and the distribution of light on vertical sur- 
faces often are important. (See Fig. 10-68.) 



. jf . , ^,^.,^ 




FIG. 10-68. In many industrial areas the visual problems occur on vertical as well 
as horizontal planes. In such cases uniform illumination should be provided on the 
vertical. 

Quality of illumination: color. With equal illumination (footcandles) 
variations in color quality of light have little or no effect upon the visibility 
of tasks that do not involve color discrimination. However, in certain 
industries color discrimination is important and in these the spectral quality 
of the light on the work may be critical. Some manufacturers paint sta- 
tionary and moving parts of machines different colors to increase contrast 
and prevent accidents. 

Quantity of illumination: recommended levels. The illumination recom- 
mended for an installation depends upon the seeing task. The degree of 
accuracy required and the size of detail to be observed, the color and re- 
flectance of task and surround materially affect the brightness distribution 
required for optimum seeing. As illumination on a task is increased, its 
brightness and the ease, speed, and accuracy with which it can be accom- 
plished usually are increased. 

Surface brightness measurements may be made with a brightness meter 
(see Section 5). Brightness may be computed by multiplying the illumina- 
tion by the reflectance of the surface. 



INTERIOR LIGHTING 10-97 

Most of the recommended illumination levels in Appendix Table A-l 
apply to the average room. If it is desired to determine the level produced 
by an existing installation, the measurement procedure outlined in Section 
5 should be followed. 

The majority of the recommended values of illumination shown in Table 
A-l refer to the general lighting measured on a horizontal plane 30 inches 
above the floor. In some cases where an illumination level of more than 
50 footcandles is necessary, it may be obtained by a combination of general 
lighting plus supplementary lighting at the point of work. 

The Illuminating Engineering Society in recent years has been studying 
the illumination needs of specific industries. If a more detailed discussion 
of the lighting specifications for a specific process is desired than it has 
been possible to include in the handbook, the reports referred to should be 
consulted. 

To ensure that a given illumination will be maintained (even where con- 
ditions are favorable) it is necessary to design the system to give initially 
at least 25 per cent more light than the required minimum. In locations 
where the dirt will collect rapidly and where adequate maintenance is not 
provided, the initial value should be at least 50 per cent above the minimum 
requirement. ■ 

Where safety goggles are worn, the light reaching the eye is likely to be 
materially reduced and the general level of illumination should, therefore, 
be increased accordingly in these locations. 

General Lighting in Industry 

Modern industrial lighting practice is to provide a uniform illumination 
level throughout every work area. This is called general lighting. The 
general-lighting level should be uniform so that light will be available, 
when needed, at any point. This is particularly desirable for interiors 
where the production layout may be changed. If the general lighting 
has been designed for uniform illumination, tables, machines, and con- 
veyors often may be moved without necessitating a change in lighting 
installation. 

The purpose of a general-lighting system where there is also supple- 
mentary lighting is to keep the brightness ratios between the task and 
the surround within a range that is comfortable to the eyes (not over 10 
to 1) in order to provide sufficient light for safety and to illuminate second- 
ary visual tasks. 

Luminaire Spacing and Layout 

The lumen method of design described in Section 8 is used to design 
general-lighting installations intended to provide reasonably uniform il- 
lumination over a given area. The footcandle level calculated by this 
method is the average for the entire area. The level in a well-designed 
system at any specific point near the center of the room may vary 5 per 
cent even in an empty room with no equipment or other obstructions. 



10-98 



I E S LIGHTING HANDBOOK 



The variation may be as great as 30 per cent if points next to the walls are 
considered, unless special attention is given these areas. 

Layout suggestions. The conventional arrangements of electrical outlets 
for lighting (one, two, or four per bay) have been adequate for a wide 
range of footcandles because of the many incandescent-filament lamps 
available in the 150- to 1,500- watt range with outputs of from 2,600 to 
33,000 lumens each. By comparison, the fluorescent-lamp range, encom- 
passing only a few ratings between 15 and 100 watts with outputs of 495 
to 4,400 lumens each, is limited. To obtain a lumen output per fluorescent 
luminaire comparable with that of a 500- or 1,000- watt, incandescent-lamp 
luminaire, it is necessary to use many lamps. 

Fluorescent lamps, by virtue of their tubular form, suggest new layout 
and installation methods: continuous rows of lamps and "troffer" systems. 
Since the lamp lengths and ballasts are different for each of the fluorescent 
lamp sizes, these lamps are not interchangeable. However, future increases 
in illumination may be provided for by a wiring layout that will accommo- 
date added luminaires or rows of luminaires to co-ordinate with the original 
installation. (See Fig. 10-69.) It is possible, also, in some two-lamp 
luminaires to add a third lamp of the same size, with an increase in illumina- 
tion of approximately 50 per cent. Where such luminaires are spaced 
closely, or in continuous rows, the two extra lamps in adjacent luminaires 
can be served from a two-lamp ballast located in one of them. Two-lamp 
industrial units with reflectors punched for lampholders for a third lamp 
are used. This potential capacity may serve several useful purposes. By 
adding the third lamp almost 50 per cent increase in illumination may be 
made available over a small area for especially difficult visual tasks, or 
throughout the installation for a general increase in illumination. Il- 
lumination levels from a general-lightin"; system are low near walls when not 




FIG. 10-69. This luminaire installation is arranged to minimize the complexity 
and expense of future increases in illumination. Spacing plan permits addition of 
units without disturbing existing installation. 



INTERIOR LIGHTING 10-99 

supplemented by natural light from Avindows. The latter cannot be de- 
pended upon at all times. It is possible to compensate for the daily and 
seasonal variations in natural illumination by using the third lamp in out- 
side end rows and in the two end reflectors of the rows between. In large 
installations this can be accomplished by having all the luminaires in out- 
side bays fitted with a third lamp. In incandescent systems, lamps of 
higher wattage than in the center of the room should be used in 
the outer bays. 

Mounting height. For practical purposes the average illumination level 
produced by general-lighting installations of spread distribution lumi- 
naires in large areas (room index > 5) is independent of luminaire mounting 
height. In small areas the average varies in proportion to the coefficient 
of utilization, not inversely with the square of the distance from luminaires 
to illuminated plane. Spacing between luminaires usually should not 
greatly exceed their mounting height. 

Supplementary Lighting in Industry 

Extremely difficult seeing tasks require illumination levels which are 
not always easily or economically obtained by standard general-lighting 
methods. To solve such problems supplementary luminaires often are 
used to provide high levels for small or restricted areas. Also, they are 
used to provide a certain brightness or color, or to permit special aiming or 
positioning of light sources to avoid shadows caused by workmen or ma- 
chinery. A reasonably comfortable interior usually results when the gen- 
eral-illumination level is at least one-tenth that of the supplementary 
level. Employees using their eyes for critical visual tasks glance away from 
their work at frequent intervals for momentary relaxation. If the bright- 
ness contrast between task and surround is too great, instead of being 
rested, the eyes are fatigued. 

Supplementary luminaires. Two types of supplementary equipment will 
take care of almost all requirements: (1) Small, concentrating projectors 
augment the general lighting on a seeing task and provide directional 
quality. (2) Large-area, low-brightness diffuse sources may provide 
either general lighting for small areas or "plus" lighting for a more difficult 
seeing task such as inspection. (See Fig. 10-70.) All supplementary 
luminaires and projector lamps should be shielded, louvered, or mounted 
so as to minimize the possibility of glare. Where adjustable fluorescent 
luminaires are used, they should be of the two-lamp type to minimize 
stroboscopic effects. 

Portable luminaires. Portable equipment can be used to good advantage 
in airplane hangars and garages and wherever internal surfaces must be 
viewed. A typical unit consists of five angle-reflector luminaires mounted 
on a portable rack with outlets for electrical tools. Two-hundred-watt, 
inside-frosted incandescent lamps are recommended. A "trouble light" 
consisting of 50- or 100- watt rough-service lamps in a guarded socket 
attached to an extension cord often is provided for internal inspection. 
Similar devices have been developed for fluorescent lamps. 



10-100 



I E S LIGHTING HANDBOOK 




FIG. 10-70. Typical supplementary- and portable-lighting equipment designs 
Portable-lighting equipment often is useful for repair work and for increasing illumi- 
nation on surfaces which are inaccessible and not reached by general lighting. 



Hazardous locations. Vapor-proof, explosion-proof, and dust-tight 
uminaires each are designed for a specific type of location where either 
corrosive vapor, inflammable gases, or explosive dusts are likely to be en- 
lcountered from such processes as oil refining, paint and varnish making, 
or lacquer spraying. (See Fig. 10-71.) Special equipment such as this 
usually is mandatory also in locations with moisture-laden atmospheres 
such as steam processing, engine rooms, and shower baths. The National 
Electrical Code requires the use of these special types of luminaires in cer- 



INTERIOR LIGHTING 



10-10) 




VAPORTIGHT 
GLASS GLOBE" 



GLASS 
REFRACTOR 



FIG. 10-71. Luminaires for hazardous locations: a. dust-tight; b. vapor-proof; 
c. explosion-proof. 

tain areas. Both angle and symmetrical types of reflectors in the 75- to 
500-watt size range are used. 

Lighting for Industrial Inspection 

In most production processes there are one or more inspection operations 
that involve checking some characteristic of a material or product against 
a previously established specification or standard. Although inspection 
or checking sometimes is accomplished by the use of devices requiring little 
visual effort or skill on the part of an operator, acceptance or rejection 
often depends on the accuracy of the visual observations of a skilled in- 
spector. Usually, because of the importance of the inspector's decisions 
in such cases, it is worth while in planning a lighting installation to treat 
an inspection area as a special problem. The following examples suggest 
ways in which a variety of typical inspection problems have been solved. 

Highly polished surfaces. Chrome or tin plate, aluminum sheet, and 
other specular surfaces frequently are inspected visually to detect scratches, 
dents, bare spots, and other flaws. It has been found that an inspector 
can locate such flaws when he views an image of a low-brightness luminaire 
in the polished surface. The image should be at least as large as the area 
to be inspected and its brightness should be not more than 400 footlamberts. 
(Surround brightness should be not less than 1/10 image brightness.) The 
area to be inspected should be so screened that images of other sources, 
windows, machinery, or personnel are not in the inspector's field of view. 



10-102 



I E S LIGHTING HANDBOOK 




FIG. 10-72. Flaws such as grind 
marks in highly polished surfaces form 
distorted images of regular patterns 
superimposed on the low-brightness 
surface of the inspection table or in- 
spection luminaire. They may be 
detected easily by this method. 



Opaque bands of uniform width 
equally spaced in parallel lines, rec- 
tangular grids, or concentric circles are 
of assistance in detecting surface con- 
tour irregularities. These are revealed 
by a distortion of the image pattern 
which in some cases may be notice- 
able only when the inspector moves 
his head. (See Fig. 10-72.) 

Printers' imposing stones, type com- 
position cases, and metals used for 
scribing present similar seeing problems 
which may be solved in this manner. 

Refractive flaws in transparent ma- 
terials may be detected by viewing the 
image of such a source or the source itself through the material. 

The following rules of thumb are applicable to the inspection of plate glass : 

1. The glass should be viewed against a combination of light and dark 
areas. 

2. The light source should have a brightness of less than 1,800 foot- 
lamberts (4 candles per square inch). 

3. The light source preferably should be rectangular in shape with a 
width of 5 to 6 inches and a length of 24 to 30 inches. "With luminaires of 
this size the width of the dark spaces between should be of the order of 2 
to 3 feet. 

Trough-shaped luminaires are located approximately 6 feet behind the 
support for the glass plate. The supporting framework for the glass plate 
should be raised or lowered to bring the glass area between the eyes of the 
inspector and one or more of the luminaires. 

Open-weave fabrics and 
other translucent materials. 
The location and removal 
of any defects in open- 
weave fabrics previous to 
the final finishing process 
is accomplished best by ob- 
serving the defects in sil- 
houette against a large-area, 
uniformly low-brightness 
panel such as shown in Fig. 
10-73. The brightness of 
the panel should be suffi- 
cient to show up defects. 
It should not exceed 400 
foot lamberts. The sur- 
round brightness should not 
FIG. 10-73. Low -brightness source for silhouette v , ., 1/10 ,, . f 

inspection of translucent materials such as fabrics, De iess Inan i / iU / na ; 0I 
glass, plastics, paper, liquids, etc. the panel. For the best 




INTERIOR LIGHTING 10-103 

silhouette vision the illumination on the cloth from the observer side times 
the reflectance of the cloth should be not more than one-tenth the bright- 
ness transmitted by the cloth. 

Light transmitted through translucent materials such as glass, paper, 
plastics, and liquids also may reveal certain kinds of faults, foreign material, 
and defects. Large luminous panels can be built in conveyor lines over 
which, or past which, the material flows. The illumination level required 
varies with the task. A panel brightness of the order of 100 footlamberts 
often is adequate. Bubbles, blisters, cracks, chips, and whorls may be 
revealed as highlights or distortions caused by refraction when transparent 
materials such as glass jars, bottles, bulbs, clear plastics, etc., are seen 
moving before a large-area, low-brightness panel. Alternate dark and 
luminous backgrounds or black strips laid on a luminous background aid 
in locating and identifying defects. 

To detect small fire cracks and bubbles in glass jars and the pin-point 
bubbles caused by foreign material in carbonated beverages, a narrow beam 
source is recommended. The mirror action of these defects reveals their 
presence. 

A modification is the arrangement employed for the inspection of inner 
tubes for air leaks. The partially inflated tube suspended from an over- 
head conveyor is passed through a trough filled with water under the sur- 
face of which there are light sources on each side of the inspector's stand. 
Any air bubbles coming from the tube are made visible by the light they 
refbct. 

Polarized illumination. The detection of internal strains in glass, 
mounted lenses, lamp bulbs, radio tubes, transparent plastics, etc., may 
be facilitated by transmitted polarized light. The nonuniform spectral 
transmittance of strained areas causes the formation of color fringes that 
are visible to an inspector. With transparent models of structures and 
machine parts, it is possible to analyze strains under operating conditions. 

Nonspecular materials. Surface flaws, irregularities in surface shape, pit 
marks, scratches, and cracks in nonspecular or mat materials are most 
easily seen by lighting which strikes the surface obliquely in such a manner 
that nonuniform surface contours cast shadows. Wrinkles in roofing 
materials are revealed by small shadows which the wrinkles cast when the 
sheet is illuminated by a narrow light beam incident at a grazing angle. 

Directional light also has been found useful for the inspection of sand- 
paper and Venetian blinds. (See Fig. 14-6.) The light may be specular 
for inspecting mat surfaces, but should be diffused at the source for ex- 
amining polished or shiny materials. 

Minute details and high precision. Careful inspection of very small 
objects may be greatly simplified by viewing their magnified images. For 
production work the magnified image may be projected on a screen. Be- 
cause the projected silhouette is many times the actual size of the object, 
any irregular shapes or improper spacings can be detected readily. Similar 
devices are employed for the inspection of machine parts where accurate 
dimensions and contours are essential. One typical device now in common 
use projects an enlarged silhouette of the teeth of a gear on a profile chart. 



10-104 I E S LIGHTING HANDBOOK 

The meshing of these production gears with a perfectly cut standard is 
examined on the chart. 

Color control and classification. Many manufacturing operations in the 
paint, lacquer, enamel, dye, textile, paper, tile, and printing fields include 
careful color-control procedures. Section 4 includes detailed discussion of 
these problems. 

Moving parts. It is sometimes necessary to inspect and study moving 
parts while they are operating. This can be done with stroboscopic il- 
lumination which can be adjusted to "stop" or "slow up" the motion of 
constant-speed rotating and reciprocating machinery. Stroboscopic lamps 
give flashes of light at controllable intervals (frequencies). Their flashing 
can be so timed that when the flash occurs, an object with rotating or 
reciprocating motion is always in exactly the same position and appears to 
stand still. 

METAL WORKING 

Some very difficult seeing tasks are encountered in metal- working shops. 
The difficulties are a result of many different causes, including the following : 

1. Low-reflectance metal surfaces result in low task brightnesses. The 
rapid collection of oil and dirt further reduces reflectance and makes good 
maintenance difficult. 

2. Work and machine surfaces are of similar character and reflectance 
and consequently provide poor contrasts. 

3. Specular metal surfaces in the process of fabrication form images 
of luminous areas in the surround. 

4. Much metal-working machinery is bulky, and obstructs the distribu- 
tion of light flux. 

5. Dimensional tolerances often are extremely narrow. 

In many industrial processes the seeing task may be greatly facilitated 
by painting various parts of the working areas, including the machines, 
in contrasting colors of good reflectance. (See Section 4.) 

Lighting for Heavy Industry 

The heavy-industry type of metal working is done in foundries, steel 
and iron mills, and fabrication assembly plants in the manufacture of such 
products as ships, locomotives, engines, turbines, structural steel, and 
automobile bodies. This work is carried on in high-bay buildings covering 
large areas. Materials are moved from place to place by means of traveling 
cranes. General illumination usualh^ is provided by high-bay luminaires, 
employing a high output light source such as the incandescent lamp or high- 
intensity mercury lamp. (See Fig. 10-74 and Fig. 10-75.) Incandescent- 
and mercury-lamp combinations sometimes are installed on alternate out- 
lets. The illumination from this arrangement is whiter than that of either 
source alone; radiation from the incandescent alone is yellowish and from 



INTERIOR LIGHTING 



10-105 



the mercury alone bluish green. Twin 
reflectors, one for an incandescent 
and one for a mercury lamp, frequently 
are mounted side by side in order that 
the radiation from the two sources will 
be more uniformly blended. 

For mounting heights of 20 feet or 
less, current practice is to use fluores- 
cent-lamp luminaires. Where possible, 
when fluorescent-lamp luminaires are 
used to provide general lighting, they 
should be installed in rows or rectan- 
gular patterns. Such a system is 
independent of subsequent rearrange- 
ment of machines and work areas. 

Even with the best general illumin- 
ation, some supplementary lighting 
frequently is required. Supplementary 
luminaires may be fastened to vertical 
columns, to side walls, or to a ma- 
chine. (See Fig. 10-76 and Fig. 10-77.) 




FIG. 10-74. Fifteen-hundred-watt 
incandescent lamps on 16-foot centers 
35 feetabove the floor in this press, 
room provide a level of 30 footcandles.' 




FIG. 10-75. High-bay area lighted with 3-kilowatt mercury lamps in open re- 
flectors. 



10-106 



I E S LIGHTING HANDBOOK 



For areas where manufacturing operations are subject to periodic or 
frequent changes, several flexible wiring systems have been developed that 
make possible convenient regrouping of luminaires. One type utilizes 
raceways from which movable luminaires are suspended. Power is drawn 
from enclosed copper busbars through sliding contacts. 

Disconnect and lowering hangers are available for the mounting of 
luminaires when, because of height or other local conditions, this type of 
installation facilitates maintenance. (See the discussion of maintenance, 
page 10-20.) 

Machine tools. Manually operated and automatic machine tools are 





FIG. 10-76 Local lighting of a large press. Four 400-watt mercury lamps in 
dust -tight angle reflectors provide 40 footcandles on the working plane. They are 
mounted 15 feet above the bed of the press. 




FIG. 10-77. The working plane 
of this punch press is lighted by an 
angle reflector locally mounted at 
the back of the press. 



FIG. 10-78. An installation of 400-watt 
mercury lamps in dust-tight RLM and angle 
reflectors along the conveyor in an auto- 
mobile-production line. 



INTERIOR LIGHTING 



10-107 




FIG. 10-79. Illumination provided by fluorescent-lamp luminaires over this 
radio-assembly line supplements the general lighting provided by the incandescent- 
lamp diffusing globes. Approximately 100 footcandles are provided on the work. 



best lighted with extended sources. Lamps in large low-brightness lumi- 
naires produce larger highlights in highly polished surfaces than do those in 
small high-brightness luminaires. 

Deep-boring operations frequently require supplementary illumination 
provided by adjustable luminaires. 

Production-line assembly. In production-line assembly each worker 
must complete his task within a limited time. Often the large number of 
people concentrated in a given area makes the shadow problem serious. 
Current practice is to treat such assembly areas as local lighting problems. 
When most of the seeing tasks are on a vertical plane, or on both vertical 
and horizontal planes, rows of luminaires mounted slightly behind the 
worker and at an angle are used. Where the seeing tasks are primarily on 
the horizontal plane, continuous rows of luminaires are mounted relatively 
close above the work along the entire length of the line. 

Many types of lamps can be used successfully for lighting assembly lines. 
(See Fig. 10-78 and Fig. 10-79.) 

Bench work. Many precision operations require handwork at a bench. 
Fixed luminaires mounted over a bench usually are satisfactory, but for 
some tasks adjustable luminaires may offer advantages. 

FOUNDRY LIGHTING 

The lighting requirements for foundry operations are about the same 
whether the worker is making nonferrous metal, steel, or gray and malleable 
iron castings, or whether the foundry is large and highly mechanized or 
small and designed for job-lot work. Recommended levels of illumination 
for foundries are given in Appendix Table A-l. Many operations such as 
molding and core making involve nonspecular-surface seeing tasks. In 
areas where such work is done, high-output luminaires can be installed 
high above the floor without introducing glare. Smoke and steam cause 
maintenance problems that are minimized through the use of the smallest 
practicable number of easily maintained luminaires. 



10-108 I E S LIGHTING HANDBOOK 

Core making. The seeing tasks involved in core making are: 

1. Inspection of the empty core box for foreign material. 

2. Inspection of the core-box sand filling for holes and other flaws. 

3. Trimming fins and wire after baking, to finish the cores. 

Two types of core boxes are in common use. One is made of metal and 
the other of wood. Each type presents its own seeing problem. The 
metal box has a specular finish. A low-brightness luminaire is recom- 
mended. The wooden core box usually is painted black or varnished and 
has about the same reflectance as sand and therefore does not contrast 
with it. 

In designing the localized-general lighting systems recommended for core 
making, the luminaires are placed with their center line directly over the 
edge of the bench used by the worker in performing the operation. This 
minimizes reflected glare and shadows. 

Molding area. The sand mold is formed by packing treated sand in a 
flask about a pattern or it may be assembled entirely from sand cores pre- 
viously formed and baked. The pattern is withdrawn after packing to 
form a cavity in the sand. Sand cores are then placed within the mold to 
complete its preparation. The flask comprises upper and lower halves 
which, when assembled, form an enclosed cavity into which molten metal 
is poured. 

The seeing tasks involved in forming molds from treated sand are : 

1. Inspecting the pattern for foreign material. 

2. Setting the pattern in the flask and packing sand around it. 

3. Removing the pattern and inspecting the mold for loose sand and for 
accuracy. 

4. Inserting cores; operator must be able to see the core supports. 

5. Smoothing mold surfaces, checking core position, and checking clear- 
ance between parts. 

Where sand is supplied from overhead ducts and conveyors, localized 
general lighting is recommended. Where there are no overhead obstruc- 
tions, a general-lighting system should be used. 

Charging floor. The weighing and handling of metal for charging fur- 
naces is a simple visual task. General illumination should be provided on 
the charging floor. 

Pouring area. The pourer must see the sprue or pouring basin in the 
mold in order to direct properly the flow of the metal. The low reflectance 
of the sand sometimes is offset by placing white parting sand about the 
opening in order to increase contrast and improve visibility. When weights 
are used, the opening in the weight indicates the general location of the 
sprue. A general-lighting system is recommended. 

Shake-out area. In the shake-out area, the operator handles flasks and 
castings. Sometimes, he must also remove the flares and risers from the 
castings. A general-lighting system is recommended, but if a ventilation 
hood is employed over the grate, supplementary lighting is required on 
the grate. 



INTERIOR LIGHTING 



10-109 



Grinding area. In grinding the operator removes excess metal and fins 
from castings, grinding to contour, to a mark, or to a gauge. Protective 
glasses worn by the operators often become fogged. The seeing task is 
fairly severe. For hand- and swing-grinder operations, a general-lighting 
system is recommended, for stationary grinders, a combination general- 
and-supplementary-lighting system. Good practice for stationary grinders 
is to locate the center line of the luminaires approximately 6 inches from 
the edge of the wheel on the side toward the operator. 

Sand-blasting or cleaning area. Three methods are used for cleaning 
castings : 

1. Sand blasting in a blast room. 

2. Sand blasting in a cabinet or on a rotary table. 

3. Friction in a tumbling barrel. 
The principal visual tasks are: 

1. Handling castings. 

2. Directing the blast stream (when manual). 

3. Inspecting the castings to see that they are clean. 

For lighting large sand-blast houses, a general-lighting system is recom- 
mended. Luminaires should be located on the outside of the room direct- 
ing light through protecting glass plates in the ceiling or walls so as to be 
accessible for maintenance. 

Chipping area. The dripper's job is to remove excess metal such as fins 
from castings. A general-lighting system is recommended. 

Inspection area. Inspection tasks are as varied as the multitude of 
products that pass through the foundry. The inspector must determine 
if castings are complete, if they have slag holes, or if there are cracks caused 
by improper cooling, sand holes, cold shuts, and blows, and he must correct 
surface appearance and correct match. The detection of cracks is the most 
difficult seeing task. 

Some inspection operations are very 
simple and do not involve fine detail 
or accurate discrimination. For more' 
precise inspection, light should be 
well diffused to minimize shadows in 
cavity and cored molds. The lumi- 
naires should be of large area and low 
brightness and should be located over 
the inspection bench or area. Either 
a "light hood" luminaire or a two- 
directional grid layout of linear lumi- 
naires may be used. (See Fig. 10-80.) 
Deep cavities and tubular areas may 
require the use of small, shielded por- 
table luminaires. 

Yard lighting. Narrow-beam, incan- 
descent-lamp reflectors, mounted either F J a l°^°- .Wse-area, low-bright- 
,, ., r. ., I ., ,. ness luminairejmstallation for foundry 
on the sides of the buildings or on chipping and inspection area. 




10-110 



I E S LIGHTING HANDBOOK 



fences, poles, or steel towers are used for lighting industrial yards. Any 
equipment exposed to the weather should be enclosed for protection 
against moisture and dirt. A mounting height of 30 feet usually is con- 
sidered a minimum. When very narrow beam projectors are used, careful 
aiming and overlapping is required to eliminate shadows. Street-lighting 
reflectors or refractors with widespread light distribution are used also. 

TEXTILES 

The seeing tasks in the textile field include both simple ones and some 
of the most severe found in industry. Recent improvements in various 
kinds of textile machinery and methods have increased its productivity, 
but at the same time have increased the severity of many visual tasks. 
For example, in some weaving sheds one weaver now may operate as many 
as thirty-six looms and it is necessary for him to see quickly and accurately. 
The lighting requirements are determined by the color, weave, and fineness 
of the material being fabricated as well as by the specific operation under 
consideration. Textile operations can be classified into three groups ac- 
cording to the type of fabric involved: (1) cotton, (2) silk and synthetic 
fabrics, and (3) wool. 

Cotton Mill Lighting 

Such operations as opening, mixing, picking, carding, and drawing can 
be carried out in a satisfactory manner if uniform general illumination of 
the order of 10 to 15 footcandles is provided. Luminaires for several types 
of fluorescent and incandescent lamps can be used successfully. (See Fig. 
10-81.) The incandescent-lamp type often is used because of its low 
initial cost. 




FIG. 10-S1. Typical cotton-mill lighting installations for: a. carding operation; 
b. drawing operation. 



INTERIOR LIGHTING 10-111 

Operations such as stubbing, spinning, spooling, and warping present 
more severe seeing tasks. The basic seeing task in all of these operations 
is to detect broken ends as soon as the break occurs and to make immediate 
repairs. Loss in production is a result of stopping an entire machine while 
repairs are being made on one thread. A minimum illumination level of 20 
footcandles is recommended for these tasks. Although general Ugh ting 
is needed to minimize contrasts, most of the light is concentrated on the 
working area. Most of the work areas of these machines are relatively 
long and narrow. A linear source aids in the elimination of shadows and 
has the desired light distribution characteristics. 

Drawing in. This is probably the most difficult seeing task in the mill 
because of the small size of the details to be seen and the unrelenting visual 
concentration required. In this operation, the warp ends are drawn by 
hand through drop- wires, harnesses, and reeds "with a thin instrument 
called a reed hook. At any one time the operator's attention, as he moves 
from one side of the warp to the other, is confined to a space about 4 inches 
square. This task requires a minimum of 100 footcandles of well-diffused 
illumination such as would be provided by fluorescent luminaires of the 
two 40-watt lamp type hung over the operator's head and aimed at the 
work. Another satisfactory solution of this problem is to use a 60- or 
100-watt incandescent lamp in an industrial reflector of parabolic shape, 
designed to be moved from one side of the frame to the other as the work 
progresses. Whichever system of local lighting is used, the surrounding 
areas should be uniformly illiiminated to a level of at least 10 footcandles. 

Automatic tying in. The ends of a full loom beam are tied to the ends 
of a loom beam which is nearly exhausted, whenever possible, in order to 
eliminate the drawing-in operation. The work lies primarily on a hori- 
zontal plane. Prolonged visual effort is involved, and localized general 
illumination of 50 to 100 footcandles should be provided. A diffusing 
luminaire similar to the industrial fluorescent type or a special local incan- 
descent type should be supplied for each operator. 

Weaving. Weaving involves visual tasks of various degrees of difficulty. 
The warp strands which run lengthwise of the cloth are drawn through the 
eyes of heddle wires which create the bobbin shed. Illumination has to 
be furnished for the "fixer" to repair and oil the loom, for the "cleaner" 
tobrush away lint, for the "creeler" to fill its bobbin creel, for other operators 
to install the full loom beams with accessories, and for still others to remove 
the full cloth roller. Broken ends must be located and "pulled in" (re- 
paired), defects in the cloth must be "picked out" (removed by picking- 
out the yarn from the filling bobbin) and the cloth must be inspected as it 
is woven. The most difficult of these tasks in the manufacture of gray 
goods is to see the detail of the finished cloth well enough to determine 
whether or not all of the specifications for perfect material are being met. 
(See Fig. 10-82.) More difficult tasks are met when weaving dark 
materials. 

The looms are designed to stop automatically when an end breaks; how- 
ever, there are defects which are not the result of a broken end. It is 



10-112 



I E S LIGHTING HANDBOOK 




FIG. 10-82. Typical weave-shod lighting installations. 

possible also for ends to break and cause a defect without the drop wires 
falling and stopping the loom. These more obvious flaws must be noted 
in addition to the smaller ones, such as a bent reed, too many ends through 
one opening between the reeds, lint on the back of the loom which will in 
time cause a break, etc. 

Shadows are a real problem in a weave shed. Light sources in the back 
aisle cast machine shadows on the work; those centered on the loom over 
the work aisle may cast shadows of the weaver's head. The ideal location 
for the luminaire is directly over the loom. To soften shadows, the lumi- 
naire should be large in area. A standard dome-type reflector, mounted 
over each loom, has been found satisfactory. One luminaire mounted 
over the work alley between each pair of looms has some advantage in 
initial cost; however, the resultant illumination is less desirable because of 
the increased possibility of shadows. 

Inspection. Inspection is a specialized task peculiar to each mill. A 
minimum illumination level of 50 footcandles is recommended and higher 
levels often are desirable. 



Silk and Synthetic Fiber Plants 

Soaking and fugitive tinting. Preparatory to twisting or throwing, 
yarns which are received in the form of skeins are soaked or lubricated. 
Also, they may be fugitive-tinted during the same operation. Tints are 
used to identify the direction and amount of twist and occasionally to 
distinguish different lots of yarn. 

The soaking operation may be carried out in a number of different ways; 
the simplest is to submerge a number of skeins in a tank of soaking solution. 
It is not necessary to see the individual threads, and the visual effort re- 
quired during the process is not great. Uniform illumination should be 
provided throughout the entire working area. The minimum level recom- 
mended is 10 footcandles. Either incandescent- or fluorescent-lamp 
luminaires are satisfactory. 



INTERIOR LIGHTING 10-113 

Winding or spooling. Each skein is mounted on a light wooden or 
wire-wheel-shaped frame, known as a swift, from which the thread is 
wound onto a horizontal friction-driven spool. The machines, which 
may be of either single- or double-deck construction, normally are arranged 
in rows. Single-deck machines usually are used unless floor space is at a 
premium. 

When the thread is broken during the winding operation, the ends must 
be found against a background consisting of the rest of the thread on the 
skein and the spool. Since the contrast is extremely low, the visual task 
is very severe and touch is relied upon to a very large extent. 

Thirty footcandles is the minimum recommended illumination for the 
spool and the portion of the swift which normally is in the field of view. 
This level can be provided by locating the light source in the center line 
of the aisle between the machines. Either a trough reflector or industrial 
diffusers may be used. Both incandescent- and fluorescent-lamp lumi- 
naires have been found satisfactory . 

Doubling and twisting. The seeing problem is similar to that in winding. 
Good illumination is needed throughout the entire length of the threads 
from their origins on the spools of untwisted thread to their terminations 
on the receiving bobbin. The machines ordinarily are arranged in rows, 
but are higher than winding machines. The lighting requirements, which 
are similar to those for winding, although in many cases considerably more 
severe, may be met with either a direct-lighting trough reflector or with 
closely spaced industrial diffusing units. A level of not less than 30 foot- 
candles is recommended for white threads and 60 to 90 footcandles is 
recommended when work with colored thread is involved. Most twisted 
yarns are fugitive-tinted. 

Conditioning or setting of twist. It is not necessary to see individual 
threads. The seeing problem is not difficult. General illumination of not 
less than 10 footcandles is recommended throughout the working area. 

Rewinding. The visual requirements are similar to those of winding or 
twisting. An illumination of 30 footcandles or more for high-reflectance 
threads is recommended, and from 2 to 3 times this value for low-re- 
flectance threads. The same type of installation as for winding is recom- 
mended. 

Coning. The lighting problem is much the same as that involved with 
other types of throwing machinery, except for the existence of the aisle 
giving access to the rear of the machines. At least 30 footcandles is 
recommended for work with light threads, and from 50 to 100 footcandles 
for work with colored threads. A diffusing type of luminaire is recom- 
mended. 

Quilling. Light should be supplied on the spool or cone from which 
the thread is being wound, on the quill on which it is being received, and 
on the entire length of the thread between them. The thread must be 
seen against a low-reflectance background, consisting of various parts 
of the machine. An illumination of not less than 30 footcandles is recom- 
mended for white threads. When dark or tinted threads are used the 
illumination should be from 50 to 75 footcandles. 



10-114 



IES LIGHTING HANDBOOK 



Warping. The spools necessary to supply all the warp ends required 
for a single section are mounted on the creel and are threaded through 
the appropriate spacing devices (reeds) and tension-control apparatus. 
(See Fig. 10-83.) All the ends in one section are gathered together in a 
single knot and hooked to a pin on the reel. As the reel rotates, the 
yardage is indicated on a large dial. After a section has been completed, 
knotted, and tied, the next section is placed on the reel alongside the first 
by exactly the same process until the required number of warp ends has 
been obtained. 

Through the action of drop wires at the top of the creel, the machine 
will stop automatically if an end breaks or the tension fails. If the break 
occurs at the creel, it usually is possible to locate both ends and splice 
them directly, but if it occurs at the reeds, the location of the end on the 
creel is somewhat more difficult. 

Good illumination on the creel is necessary to enable the operator to 
locate and repair the broken ends and to place new cones, the threads of 
which must be tied to the ends of the threads on the cones in use. 

The recommended illumination at the top of the creel is 50 footcandles 
or more, with the greatest practicable uniformity throughout. 




— "— ' " ".•///•//.■ '."^'/vv^ /V ;Avyy/ 1 ^/..'. ■'/;;///?/////////////////// 



REEL 



■0- 




FIG. 10-83. Plan and elevation of inclined-creel silk warper. 



INTERIOR LIGHTING 



10-115 



8 FT COTTON 
9 FT RAYON 



WEAVE AISLE 



BEAM AISLE 



Drawing in or entering. Throughout the entire process it is necessary 
to see the threads against a low-reflectance background comprising the 
mass of heddles. The seeing task is very severe for both operations. 
Accordingly, the illumination recommended in the plane of the heddles is 
100 footcandles or more. General illumination supplemented by con- 
centrating luminaires may be used. The concentrating luminaires should 
be fixed in position and should illuminate the entire working area without 
repeated adjustments by the worker. 

Weaving. Weavers are constantly 
on the alert to see that looms are 
producing according to specifications. 
A loom may continue to operate 
after an end has been broken if the 
drop wire fails to fall . Other causes, 
such as a bent reed, produce defects 
which can be determined only by 
an inspection of the cloth. These 
defects should be located as soon 
as they occur so that corrections 
can be made and high shrinkage 
losses avoided. 

Recommended illumination levels 
for silk and synthetic-fiber weav- 
ing are 30 footcandles for high-re- 
flectance and 50 to 100 footcandles 
for low-reflectance threads. (See 
Fig. 10-84). 

The fact that looms usually are arranged in long aisles and facing each 
other makes it possible to center the luminaires over the weave easily, 
thus illuminating the front of two looms with one luminaire. In wide- 
goods weaving, the shadow of the weaver on the loom usually is not ob- 
jectionable as he ordinarily stands in such a position that his shadow is not 
on the portion of the work under observation. 

For the back of the looms where the visual effort usually is less severe 
and not so prolonged, one luminaire (of the same lumen output) per four 
looms, with a higher mounting, will provide satisfactory illumination. 

Burling and mending. The object of burling and mending is to locate 
and, when practicable, remove any defects in woven cloth prior to the 
final finishing process. Several types of defects may exist: (1) broken 
filaments and knots; (2) loose filling; (3) slack or tight ends; (4) pulled 
warp; (5) temple cut, and (6) stretched yarn. 

Each of these six defects can be observed best in silhouette against a 
flashed-opal glass plate, lighted from beneath. The optimum brightness 
of the plate is a function of the transmittance of the sample, high for low- 
transmittance (opaque) materials, and low for high-transmittance (sheer) 
fabrics. 



FIG. 10-8-4. Recommended lighting 
installations for silk, synthetic -fiber, and 
colored cotton looms. The spacing of 
the fluorescent reflectors down the loom 
row will be about eight feet on centers 
for cotton, nine feet for rayon. Lumi- 
naires should be mounted about 10 feet 
above floor, preferably below humidi- 
fiers. 



10-116 



i E S LIGHTING HANDBOOK 



DIFFUSING GLASS 
ILLUMINATED FROM BEHIND 




For the best silhouette vision the illumi- 
nation on the cloth should be low. A 
brightness of one hundred to four hundred 
footlamberts for the flashed-opal glass plate 
has been found satisfactory for some pur- 
poses. The opal glass plate should be set 
at an angle of 45 degrees. Cloth is drawn 
over it at a fairly rapid rate. (See Fig. 
10-85.) 



FIG. 10-S5. A burling and 
mending table. 

Silk-hosiery knitting. This machine operation presents a severe seeing 
task. A line source installed directly above the front of the machine and 
illuminating an 18-inch strip the length of the machine to a minimum 
level of 30 footcandles in service is recommended. Luminaires should be 
at least 1\ feet from the floor. Continuous fluorescent-lamp luminaires 
or a row of five or six 200-watt incandescent lamps in dome reflectors are 
recommended. 

Woolen and Worsted mills 

The seeing problems in woolen and worsted manufacture are, if anything, 
more severe than in cotton, and are more nearly comparable to conditions 
encountered in silk and synthetic-fiber manufacture. 

Carding, picking, washing, combing, twisting, and dyeing are routine 
operations comparable to similar tasks in silk and synthetic-fiber plants. 
The minimum general illumination recommended is 10 footcandles for 
high-reflectance yarns. The level should be increased to compensate for 
low-reflectance yarns. Either fluorescent- or incandescent-lamp luminaires 
are recommended. 

Drawing in and warping. These operations present severe seeing tasks. 
A minimum illumination level of 100 footcandles provided by local diffusing 
luminaires is recommended. 

Weaving. Twenty footcandles is the minimum illumination level 
recommended for high-reflectance goods. When the yarn is dark, a 
100-footcandle level is recommended. Plants processing both light and dark 
goods should provide the higher level. Since the reflectance of wool fibers 
is diffuse, whereas that of the rayon and silk fibers is specular, the location 
of the luminaires with respect to the operator is not as critical. 

Knitting. A minimum general illumination level of 20 footcandles is 
recommended for knitting machines for such articles as stockings. 



INTERIOR LIGHTING 



10-117 



CLEANING AND PRESSING 

The operations in dry-cleaning plants are functionally divided as follows : 



6. 

7. 

S. 

9. 
10. 
11. 



Laundry or wet cleaning. 
Repair and alteration. 
Machine finishing. 
Hand finishing. 
Final inspection. 
Shipping. 



1. Receiving. 

2. Checking and sorting. 

3. Dry cleaning. 

a. Naptha-solvent process. 

b. Synthetic-solvent process. 

4. Steaming. 

5. Examining and spotting. 

Receiving. Cleaning and pressing establishments receive soiled items 
from their pick-up trucks at a receiving platform at which garments are 
transferred from motor truck to hand truck. The garments are then 
wheeled to the checking and sorting tables. The recommended minimum 
illumination level for the receiving platform and passage is 10 footcandles. 

Checking and sorting. For special instructions a checker reads a driver's 
ticket written in pencil attached to incoming garments and pins tags 
numbered in indelible ink to each garment for matching with the original 
ticket after the completed operation. Pockets are searched for matches 
or articles of value and finally the sorter divides the garments into silks 
and woolens, dark and light colored, or other classifications necessitated 
by the cleaning operation. The penciled notations are difficult to read. 
Contrast, as well as the handwriting, often is poor. The minimum recom- 
mended illumination level is 20 footcandles. 

Dry cleaning by the naphtha-solvent process. The solvent used in this 
process is inflammable and under certain conditions explosive. For this 
reason the cleaning operation is carried on in a separate building or in a 
section of the plant divided off by a firewall. Explosion-proof lighting 
equipment is mandatory. 

No attempt is made in the washing and drying room to determine whether 
the cleaning has removed all spots and no other difficult seeing problems 
are involved. A 
average 

10 footcandles is recommended. 
The explosion-proof fixtures 
must be located so the washer, 
extractor, and drying-tumbler 
interiors are well illuminated 
when the covers are thrown 
back. (See Fig. 10-86.) In 
addition, distribution must be 
such as to light properly pres- 
sure and flow gauges on the 
filters and in the piping. 
The time of washing is FIG 10 . g6 Eleyation of instalIation 

largely determined by the for the naphtha-solvent process of dry cleaning. 



minimum use iso-watt explosion 

• 1! ,• ii n PROOF FIXTURE WITH DOME 

illumination level of reflector, spacing in 

ROWS 7 TO 10 FEET 



DIMENSION VARIES WITH 

SIZE AND LOCATION OF 

WASHER OPENING 



FILTER GAUGE 

MOUNT WHITE 
> BACKGROUND 
BEHIND GAUGE 




10-118 IES LIGHTING HANDBOOK 

clarity of the naphtha coming from the washer. This, dirt can best be 
seen in silhouette against a white background while it is passing through 
the filter gauge. 

Dry cleaning by the synthetic solvent 'process. This process differs from 
the naphtha type in using a nonexplosive solvent and a closed system. 
The seeing tasks are related to loading and unloading the cylinder and 
reading the various temperature, pressure, and flow gauges. Light 
should be directed into the cy finder and toward the gauges from locations 
such that an image of the source will not be formed in the field of view. 
Examining and spotting. The dry-cleaning process takes practically 
all of the oil and grease out of stains of various types unless it is ground 
into the fabric very firmly. Nearly always, however, some spots remain 
to be taken out by water spotting. Many stains have characteristic 
colors by which they may be identified by a skilled "spotter." 

Through long experience this workman is trained to detect, classify 
as to type, and remove all types of spots after choosing the proper chemicals. 
The critical seeing task lies in detecting the spot and its type. An explana- 
tion for the usual large number of the garments rejected during final 
inspection, for most of those sent back by customers, and for many garments 
stained by chemicals during spotting, can be found in the inability of the 
spotter to see the stains and identify them. 

After the washing process, spots present a very subdued appearance 
with little contrast between themselves and the material. Also, the 
reflectance of many materials has a strong specular component. It is 
current practice for spotters to work under a screened skylight or along 
north-wall windows. Here when the weather is favorable the illumination 
level varies between 50 and 200 footcandles and the light is well diffused. 
Except on dark days and in direct sunlight, the natural illumination is 
considered satisfactory by most cleaners. Electrical illumination used 
to extend the working hours should blend well in color with daylight. 
(See Section 4.' 

A level of 150 footcandles or more provided 
by a low-brightness, large-area source is recom- 
mended. (See Fig. 10-87.) The face is covered 
with tracing cloth as a diffusing medium. A simi- 
lar luminaire containing six 100-watt daylight 
fluorescent lamps gives off less heat and can be 
made to have a more shallow cross section. 
diffusing cover Repair and alteration. Both hand and ma- 

FIG. 10-87. Large-area, chine sewing is done in this section, often with 
low-brightness luminaires dark thread on dark material. For hand 
are recommended for use fc genera l illumination level of 50 foot- 

over spotting tables in dry- & . 

cleaning plants. candles of well-diffused light is recommended. 

Supplementary illumination at the needle point of the machines sufficient 
to raise the level to 200 footcandles is recommended. 

Machine finishing. Machine presses usually are lined up in a row for 
convenience and for minimum cost in the steam-piping installation. The 




INTERIOR LIGHTING 



10-119 



FIG. 10-88. Plan and 
elevation of lighting in- 
stallation for machine 
finishing. 



VARY WITH 
DIFFERENT 
MACHINES 



|*^' 




ELEVATION 
<V/////////////////////////////////////////////////A . 



n □. 



n 



^ 



, — 300-WATT GLASSTEEL D1FFUSERS 
PLAN VIEW 



<> 



operator combines speed 
with good workmanship. 
Each garment is moved 
several times as a small sec- 
tion is finished and another 
moved onto the buck (work- 
ing surface) . The workman 
watches to see that all 
wrinkles are eliminated. 
The buck of the press 
should be uniformly illumi- 
nated without shadows from 
the head of the press 
or the workman's body. 
Crosslighting from two sources is recommended. (See Fig. 10-88.) This 
method takes care of the working area on the buck and in addition illumin- 
ates the clothes racks, aisles, and machine space. A minimum level of 
30 footcandles is recommended. 

One of the most difficult tasks is to prevent double creases in trouser 
legs. A concentrating reflector at the rear of the buck causes a crease to 
cast a shadow, making it more easily discernible. 

Hand finishing. Hand finishing (ironing) boards usually are installed 
in rows spaced 3^ to 5 feet apart. The volume of handwork is decreasing 
gradually because of improvements in machines. However, the hand 
iron still is used to achieve the best results on lightweight materials. The 
hand finisher watches to see that wrinkles are eliminated, that the garment 
is completely pressed, that it is not scorched, and corrects minor defects. 

The seeing task is moderately critical because careful handling of the 
iron is required for pleats, shirring, ruffles, and trimming. A 50-footcandle 
level should be provided. 

Final inspection. Garments on individual hangers are delivered to the 
final inspector on portable racks or by a power-chain conveyor. Each 
garment in turn is removed from the rack and hung on an overhead support 
in such a way that it will rotate easihy. The inspector examines the gar- 
ment carefully, watching for inferior finishing, for spots, for damage done 
to the material during the cleaning process, and for completion of any 
customer-ordered repairs or alterations. 

The owner relies on the inspector to make sure that the garments leaving 
the plant are properly cleaned and finished. Most of the critical visual 
work is done with the garment at approximately a 45-degree angle with 
the vertical and at short range. The lighting requirements are about 
the same as for spotting. A 200-footcandle level of well-diffused illumina- 
tion from a large luminaire mounted directly in front of the garment support 
and at least 8 feet above the floor is recommended. To increase the 
vertical plane illumination the luminaire should be tilted parallel to the 
usual garment plane, 



10-120 



I E S LIGHTING HANDBOOK 



Shipping. The shipping section covers the garments with protective 
paper bags, attaches the original ticket, and loads the delivery trucks. 
The identifying tags attached to the garments often are difficult to read 
because the ink is partially washed out during the cleaning process. A 
minimum illumination of 30 footcandles is recommended for the wrapping 
area and the shipping table. Ten footcandles is recommended for other 
parts of the shipping section. 

Laundry or wet cleaning. On some garments the spots are so numerous, 
large, and widely distributed that it is uneconomical to use the spotting 
method for removing them. Each cleaning plant maintains a small 
laundry for such garments. A conventional cylindrical washer, centrifugal 
extractor, and drying tumbler are used. The lighting problem is very 
similar to that of the dry-cleaning operation. Vapor-proof luminaires 
with diffusing opal glass covers and enamel reflectors are recommended. 
Luminaires must be located so as to light the interior of the machines and 
provide a level of at least 10 footcandles. 

CANDY MANUFACTURING 

In compliance with stringently enforced pure food laws and to foster 
good will, progressive candy manufacturers utilize every means for promot- 
ing cleanliness and efficient plant operation. New plants are constructed 
to utilize the greatest possible amount of daylight, but some still have 
inadequate and inefficient electric-lighting systems. 

Chocolate Making 

In the manufacture of choco- 
late, the cacao beans first are 
toasted and then are passed 
through shell-removing ma- 
chines. The bean then is con- 
veyed by gravity feed to the 
crushers which press out liquid 
cacao butter. After milling 
and mixing with powdered 
milk and confectionery sugar, 
the pulverized beans are pressed 
through a series of rollers and 
then mixed with the cacao 
butter in a conche. 

Many of these operations 
are gravity fed and utilize por- 
tions of two or three floors in 
a large plant with conveyors 
or chutes passing through the 
floors. There is very little 
handwork because practically 
all processes described are 




mmm7MW77777/M77777777777M777m777777M77777777777777/ 



FIG. 10-89. Typical five-roller refiner. 
Periodic adjustments are made at the five 
rollers. Light should be distributed so as to 
illuminate the entire refining area. 



INTERIOR LIGHTING 10-121 

confined to the inside of hoppers, refiners, conches, and other machines. Con- 
sequently, no difficult seeing tasks are encountered in chocolate manufacture. 
A level of illumination of not less than 10 footcandles is recommended 
for the chocolate-processing sections of the plant. However, 25 footcandles 
is recommended for the five rollers of the roller mill, where a careful setting 
of the rollers must be made periodically. Supplementary lighting, having 
a predominant vertical component, should be used at this point. (See 
Fig. 10-89.) 

Chocolate Dipping 

Dipping is carried on in various sections of large plants, because this 
arrangement facilitates the manufacture and minimizes the conveyance 
of the different fillings. Dipping tables generally are located symmetrically 
in the area provided, with the operator sitting beside a depressed section 
of the table. Drippings from the operator's fingers are set in a design on 
top of the candy for decoration. The dipper must see the relative position 
of the drippings from the hand over the confection in order to make a 
neat and orderly design. A diffuse, uniformly distributed illumination 
level of not less than 20 footcandles on the work should be provided in 
each dipping room. 

Cream Making 

Glucose, which is the base for most creams and fillings, is cooked, beaten 
by paddles, then remelted and recooked to increase its viscosity. It 
is then flavored, beaten again, and finally pressure-formed in plaster-of- 
Paris molds. The seeing task in cream making is of moderate severity. 
A general illumination level of the order of 20 footcandles provided by 
diffusing luminaires is recommended. 

Kiss Wrapping 

A kiss-wrapping production line consists of many individual kiss- 
wrapping machines, arranged on both sides of a belt conveyor. General 
illumination of not less than 10 footcandles should be provided over the 
entire area, with supplementary lighting of 50 footcandles at the critical 
seeing points. These vary in location with the type of wrapping machine. 

Gum Drop and Jellied Form Making 

In this process plaster-of-Paris patterns are used to make smooth molds 
of fine-milled cornstarch. The molds are arranged symmetrically in 
shallow wooden trays which then are moved into such a position by a belt 
conveyor that one row of molds is placed directly under a series of injectors 
which automatically place the proper quantity of syVup in each. This 
operation is repeated until all molds in the tray are filled. In mold-fillers 
for gum drops and similar candies, the automatic injectors which press 
the fluid candy into the molds are kept clean by an attendant. 

A minimum uniform illumination level of 20 footcandles provided by a 
concentrated source hung above the equipment and directed toward the 
molds is recommended. 



10-122 



I E S LIGHTING HANDBOOK 



Hard Candy Making 

In the manufacture of hard candy, sugar is cooked, flavored, and placed 
on water-cooled tables in a semisolid state where a batch is kneaded into 
an oblong shape. Fillings are added at this stage. The batch then is 
worked into a cylinder about 10 inches in diameter and 6 feet- long. After 
tapering in a heated canvas hammock the point is fed through a die-casting 
machine (Fig. 10-90), which automatically shapes and cuts the candy. 

Twenty footcandles of general illumination should be provided for 
ingredient mixing and cooking, and the levels should be increased by 
supplementary lighting to a minimum of 50 footcandles at the die-casting 
machine. Supplementary luminaires should be located between the 
operator and the die-cutting machine. Because of the specular reflectance 
of hard candy, luminaires with a large low-brightness luminous surface 
should be centered 4 feet above each hand-mixing table. Continuous 
fluorescent-lamp luminaires also may be used. An illumination level of 
not less than 40 footcandles is recommended. 

Assorted Candy Packing 

There are three methods of packing candy: 

1. Progressive method. In the progressive method candy is placed in 
simple containers in front of the operators who sit on each side of a long 
table along the center of which extends a belt conveyor. 

2. Stationary method. In the stationary method long flat tables, 36 
inches high and 36 inches wide, are used. Directly over the center of the 
table a stock rack, 18 inches wide, is suspended from the ceiling or fastened 
to the table so that its bottom is 18 inches above the top of the table. 
The operator removes eight or ten different types of candy from the rack 
and packs them in a box in front of her. 



LIGHT 
REQUIRED IN \ 
THIS DIRECTION \ 




TO COOLING 
CONVEYOR 



FIG. 10-90. Hard-candy-forming machine. The batch is revolved slowly in the 
canvas hammock. Heat is applied for surface glazing. The operator tapers one 
end to enter the dicing machine at point A, which cuts and forms in one operation 
and delivers the pieces to a cooling conveyor. An illumination level of 30 foot- 
candles should be supplied at point A. 



INTERIOR LIGHTING 10-123 

3. Circular metlwd. In the circular method, which is not used as much 
as the other two, a ring table, 36 inches high and 18 inches wide, is used. 
The outside diameter is about 6 feet, the inside diameter about 3 feet. 
The operator sits on a swivel stool in the center. The candy to be packed 
is placed on the circular table, one kind to a container. By rotating her 
stool 360 degrees an operator is able to pick a complete assortment. 

On the basis of visibility meter tests of all three methods, a minimum 
uniform illumination level of not less than 20 footcandles is recommended 
for the entire packing area. 

Special Holiday Mold Candy Making 

Holiday candy usually is made on the north side of the building where 
the best natural illumination is available to aid in the hand artistry generally 
required. At window tables operators with small artist's brushes decorate 
molded candy with a thin, colored mixture of cream filling. Because of the 
intricate positions in which decorations must be placed on the confection, 
and the fine details of the decorations themselves, the seeing task is severe. 
On the basis of visibility meter tests a minimum illumination level of not 
less than 50 footcandles is recommended. The color should blend with the 
daylight. 

Box Making and Scoring 

In many candy factories, containers and boxes are made on the premises 
in a department divided into two main sections, one devoted to making 
standard boxes, the other to special boxes. 

Scoring, the first operation in making boxes, is mechanical. Care must 
be taken that the frame which holds the knives in position does not cast 
a shadow on the flat cardboard surface. All light sources should be located 
between the operator and the frame of the scorer, thus avoiding shadows 
under the frame holding the scorers. 

Flat cardboard usually is fed over rollers at the front of the machine 
and the first set of scorings is made by circular knives. In manufacturing 
these boxes, scorings must be made also at right angles to the original 
scorings. A general illumination level of 20 footcandles is recommended. 

After the cardboard has been scored, it is conveyed to a box-forming 
machine. This machine bends the cardboard at the scorings, applies 
the gummed corner supports, and automatically shapes the container. 
The machine is pedal-controlled, and all work is accomplished on a hori- 
zontal plane, with the tool and forming-die completing the work. 

Most container stocks have a high reflectance compared with the machine 
background. The contrast usually exceeds 75 per cent. It is recom- 
mended that a minimum general illumination level of 20 footcandles be 
provided. 

In decorating, much silver- and gold-colored foil is used. Most decorat- 
ing operations include handwork facilitated by pedal-controlled presses. 



10-124 



I E S LIGHTING HANDBOOK 



Because of the specular reflectance of the coverings, it is recommended 
that large-area, low-brightness sources be used. 

At the tables where art work on the containers is completed, 20 foot- 
candles is the minimum recommended illumination level. 

PRINTING AND COLOR ENGRAVING 

Type Composition and Handling 

Metal type handling and color control in modern color-reproduction 
processes present the critical seeing problems which are characteristic 
of the printing industry. A printer frequently works with a slug, galley, 
or form of clean type, or with a clean engraving or electrotype plate. 
Each is a mottled metallic mirror. The raised type face usually has been 
inked at least once during the pulling of proof and therefore is darker than 
the bright specular surface of the clean shoulder. The shoulder or flat 
depressed portions act as a mirror against which the characters are sil- 
houetted for inspection. Large-area luminaires are recommended for the 
areas of the plant in which type must be assembled or proved. 




FIG. 10-91. Dark letters mounted 
on a silvered mirror (representative 
of fresh type slugs that have been 
proofed). The figure shows that 
characters are easily visible only when 
they lie within the image of a light 
source. 



Figure 10-91 shows a mirror-like sur- 
face of type metal with letters pasted 
on it and lighted by a standard in- 
dustrial reflector such as is found over 
the type cases and imposing stones in 
printing establishments. Note that of 
all the characters only those few that 
are within the reflector image are re- 
vealed. In installations with lumi- 
naires mounted 8 or more feet above 
the floor, the size of the image of this 
type of luminaire, when viewed by a 
compositor, usually is less than 4 inches 
in diameter. Many printers have dis- 
covered that if they drop the reflector to 
the lowest feasible position, they can see 
the type better. When the reflector is 
lowered, the size of its image is in- 
creased and therefore silhouettes more 
of the characters (Fig. 10-92.) 



In an ordinary type character, the edges where the bevel joins the 
shoulder and at the face are rounded by use into tens of thousands of con- 
cave and convex mirrors. (See Fig. 10-93.) 



INTERIOR LIGHTING 



10-125 



Fig. 10-92. Graphical illustra- 
tion of the value of lowering the 
ordinary factory reflector over the 
imposing stone. The ideal condi- 
tion is represented by the right- eye 
hand figure. ^ 



\ I 



J\\ 







£ 



FACE SHOULDER 



I, EYE 



// * [I ^ 



/ /// / / 

; //; // 

1 '/ v" 

r 



if/ 



14 / 



EYE 




-PLANE MIRROR 2- CONCAVE MIRROR 3- CONVEX MIRROR 



TYPE 




FIG. 10-93. Reflections from type : (above) If the light source is small in area reflec- 
tions will be glaring, (at left) In an ordinary form there are many thousands of 
tiny filets and rounded corners that act as concave and convex mirrors to reflect light 
into the eye. (at right) When a large low-brightness source is used characters 
become more legible because glare is minimized. 



10-126 



I E S LIGHTING HANDBOOK 




If the image of the luminaire is to 
cover the entire galley or form its 
area should be at least as large as the 
form and preferably should be as large 
as the stone. A luminous ceiling is 
ideal. The large luminaire shown in 
Fig. 10-93 has a 36-inch by 56-inch 
rectangular luminous area. It will be 
noted that every character on the 
several mirrors is silhouetted plainly 
against the image of the luminaire. 
Fluorescent-lamp luminaires with dif- 
fusing covers are particularly well 
adapted to this application. (See Fig. 
10-94.) 

Illumination for compositors' cases 
and imposing stones should possess the 
following characteristics : 

1. The luminaire used should have 
a low uniform brightness. This ex- 
cludes any fixture with bare or frosted 
incandescent lamps that are partially exposed in the direction of the type. 

2. The luminous area of the fixture must be large. 

3. The image of the luminaire visible to the worker should cover the 
entire form. 

4. The illumination level at the type should be not less than 50 foot- 
candles. 




FIG. 10-94. Luminaire for composi- 
tors in printing establishment. 



Machine Composition 

Linotype, Intertype, and Monotype machines usually are equipped with 
local lighting equipment by the manufacturers. Fluorescent-lamp lumin- 
aires should include two lamps operated out of phase to minimize 
stroboscopic effect. Large-area, low-brightness luminaires should be 
used to provide the minimum recommended illumination level of 30 foot- 
candles. 



Press Room 

On the bed of a typical two-revolution flat-bed cylinder press, it is 
necessary to discriminate fine detail during make-ready and register 
operations. A minimum general illumination of 30 footcandles is recom- 
mended. 

Pressmen need a large-area, low-brightness light source, such as 
recommended for the composing table and type case, but low head room 
under the feed board interferes with a simple overhead installation. 
Fluorescent-lamp luminaires also are well adapted to this application. 



INTERIOR LIGHTING 



10-127 



Color Reproduction 

All persons who are responsible for quality control in color reproduction 
should use illumination of the same spectral characteristics. A screened 
table illuminated to a level 
of 50 footcandles of con- 
stant known spectral dis- 
tribution is recommended 
for color inspection. It 
may be used with uniform, 
equally satisfactory results 
by day and night shifts. 
It should be conveniently 
located with respect to a 
group of presses. The 
screening surfaces should 
have a nonselective reflec- 
tance, that is, they must be 
either neutral white, gray, 
or black. A color-inspec- 
tion table may be combined 
with a mark-out booth. 
(See Fig. 10-95.) 




FIG. 10-95. Combination inspection and mark- 
out booth. Note eye-shield or baffle for elimina- 
tion of glare when observing type impression. 



PETROLEUM AND PETROLEUM PRODUCTS 

In oil and petroleum products manufacturing plants, various types of 
lighting equipment are utilized to provide illumination to facilitate dif- 
ferent visual tasks. When planning an installation, a maintenance factor 
not greater than 0.65 should be used unless detailed maintenance data are 
available. Numerical values of illumination recommended in the following 
paragraphs are maintained values based on this factor. 

Process Equipment Buildings 

In oil- and water-pump houses, compressor and filter buildings, etc., 
uniformly distributed illumination levels of 8 to 10 footcandles are recom- 
mended. Because of piping and equipment located near, the ceiling in 
such areas, a symmetrical layout and uniform mounting height of luminaires 
must in some cases be modified in order to prevent shadows. 

Two general types of luminaires may be used. Where locations are 
described as Class 1, Group D hazardous, explosion-proof luminaires 
equipped with strong reflectors such as shown in Fig. 10-71, or with other 
suitable types, should be used. At nonhazardous locations (pump rooms 
for processing heavy oils, etc.) in which a corrosive but nonexplosive 
atmosphere prevails, vapor-tight luminaires such as shown in Fig. 10-96 
may be employed. Luminaires within reach, or otherwise exposed to 
breakage, should be equipped with metal guards. 



10-128 



I E S LIGHTING HANDBOOK 



VAPORPROOF 
METAL BOX 




FIG. 10-96. Incandescent-lamp luminaire installation for an instrument board. 
The luminaire consists of a vaporproof metal box containing two 100-watt incan- 
descent lamps and a prismatic lens. The lens aims a fan-shaped beam at a line located 
approximately one-third of the distance from bottom to top of the instrument board. 



Instrument Boards & Individual Instruments 

Instrument boards which contain indicating and recording pyrometers, 
flow controllers, gauges, level indicators, etc., are located in most cases 
in separate control rooms. A vertical illumination level of 30 footcandles 
on the instrument portion of the board is recommended. Luminaires 
should be located directly in front of and above the instrument boards, 
and in such a manner as to minimize specular reflections from the instru- 
ment windows in the observer's field of view. Either incandescent or 
fluorescent luminaires may be used. Where hazardous explosive conditions 
may exist the air pressure within luminaires should be maintained higher 
than that in the room by means of pipe connections to a blower or com- 
pressed-air system which draws air from a gas-free location. An allowance 
of approximately 80 to 100 watts per foot width of an instrument panel 
may be required for the lighting of the panel. To meet rigid "explosion- 
proof" requirements, luminaires such as shown in Fig. 10-71 may be used. 

Individual instruments and gauges. Luminaires with angle-type re- 
flectors are recommended for lighting individual instruments. Liquid 
column gauges often have built-in luminaires or can be illuminated by 
special "gauge-light fixtures" mounted either in front or in back of the 
gauge glass. 



INTERIOR LIGHTING 10-129 

Special Equipment 

Special lighting equipment often is required, such as that for illuminating 
the insides of filters or other equipment whose operation must be inspected 
through observation ports. If the equipment does not include built-in 
luminaires, concentrating- type reflector luminaires should be mounted at 
ports in the equipment housing. 

Portable luminaires are utilized where manholes are provided for inside 
cleaning and maintenance of tanks and towers. Explosion-proof types 
(where hazardous conditions may exist) with 50-foot portable cables are 
connected at industrial receptacles (either explosion-proof or standard) 
provided near manholes on towers and at other locations. 

Outdoor Tower Platforms, Stairways, Ladders, Etc. 

An illumination level of 2 to 4 footcandles is recommended for unob- 
structed platforms, upper and lower landings of stairways, and ladders. 
Luminaires should provide uniform illumination and should be shielded 
from the direct view of persons using these facilities. On unobstructed 
platforms 150-watt incandescent lamps spaced on 12- to 18-foot centers 
usually are adequate. Special luminaires often are required at gauges. 
Vapor-proof and weather-proof luminaires equipped with refractors or 
clear vapor-proof covers may be used. Luminaires above top platforms or 
ladder tops should be equipped with refractors or reflectors. Reflectors 
may well be omitted on intermediate platforms around towers so that the 
sides of the towers will receive some illumination and the reflected light 
therefrom will mitigate sharp shadows. 

Oil heaters (furnaces). Oil heaters are tower-like and require illumination 
at their firing fronts, at their sides, and on platforms, stairs, and ladders 
attached to the heater structure. This may be provided by an installation 
of vapor-proof, incandescent-lamp luminaires (150- or 100- watt) attached 
to the structural frame, or by means of 300- or 500-watt, incandescent- 
lamp floodlight or asymmetric refractor units mounted on poles around the 
heater, or on adjoining structures where such are available. Electrical 
convenience outlet receptacles for portable luminaires are necessary for 
maintenance purposes. 

Outdoor areas around buildings and structures. Where buildings and 
structures are close together, local vapor-proof or explosion-proof lumin- 
aires mounted on brackets at doors or hung from structures, pipe supports, 
etc., are satisfactory. 

For large areas, illumination should be provided by means of refractor- 
type luminaires mounted on steel or wood poles, 25 to 35 feet above grade. 
Vapor-tight floodlights utilizing 300- to 1,000- watt incandescent lamps 
also can be used where high structures are available for mounting them. 



10-130 



I E S LIGHTING HANDBOOK 



SHOE MANUFACTURING 

Shoe-manufacturing processes may be separated into three groups ac- 
cording to the type of seeing tasks involved in each: 

1. Simple seeing tasks include: 

Leather: storage, staying, sole laying, beveling, nailing, heel scouring, 
burnishing, spraying, box making, dinking, last racks, lasting, pulling 
over, trimming, channeling, heel breasting, edge setting. 

Rubber: washing, compounding, calendering. 

2. Seeing tasks of average difficulty include the mechanized operations: 
Leather: skiving and splitting, treeing, welting, rough rounding, per- 
forating, buttonholing, eyeletting on both light and dark materials, certain 
types of bench work. 

Rubber: sole rolling, milling, completed stages of compounding. 

3. Seeing tasks of considerable difficulty include: 

Leather: cutting, bench work, stitching, inspection, rounding, sole 
stitching, fine edge trimming on both light and dark materials. 

Rubber: cutting, making, calendering. 

Recommended levels of illumination for typical manufacturing opera- 
tions are given in Table 10-15. 

Leather-Shoe Manufacturing 

Sole department. In a sole department, leather, sorted for grain and 
thickness, is stored in 5- to 6-foot piles on low platforms which are ar- 
ranged with passageways between them. A uniform illumination level of 
about 10 footcandles throughout the storage area is recommended. 

For grading according to color, some advantage may be gained by the 
use of illumination of spectral characteristics similar to daylight. 

Beam clinkers. A beam clinker stamps 
soles and insoles out of hides by means of 
dies. (See Fig. 10-97.) It consists of a 
heavy cast-iron frame and a large beam that 
exerts pressure through a vertical motion on 
a cutting die. There is some hazard of finger 
injury in operating the machine. This may 
be minimized by a localized general lighting 
installation which provides an illumination 
level of 20 footcandles on the die. 

To avoid casting shadows of the beam on 
the platform, all luminaires in the area oc- 
cupied by the beam dinkers should be placed 
at the operator's side of the machine. 

Last storage. Last storage bins usually 
are located in a segregated section of the 
sole department. Generally there is a 3-foot 
aisle between the bins. Luminaires with 
asymmetric distribution should be mounted 



<y 




*&[ 



PS? 



FIG. 10-97. Leather shoe 
manufacturing: The operator 
of a beam dinker holds a die 
and regulates pressure on the 
die with his foot. Light should 
be projected to the machine 
from the right and to the back 
of the operator to eliminate 
objectionable shadows 



INTERIOR LIGHTING 



10-131 



over the aisles so as to illuminate the bins in order that lasts may be 
selected. 

To improve the lighting in the rear of the bin, wedges of aluminum may 
be laid across and fastened to the base of each bin at the front. The sides 

Table 10-15. Recommended Levels of Illumination for Shoe 
Manufacturing 



DEPARTMENT 



FOOT- 
CANDLES 



LEATHER SHOES 



Storage and Sole Leather Department 






Leather storage 




10 


Vamp storage 




10 


Last storage 




10 


Beam dinkers 




20 


Miscellaneous areas and aisles 




5 


Cutting and Stitching 






Cutting tables 




20 


Marking, buttonholing, skiving, sorting, f 
vamping, counting \ 


Light material 


20 


Dark material 


100 


Stitching \ 


General illumination 


10 


Light material 


30 


[Dark material 


100 


Office and stock room 




30 


Making Department 






Stitchers, rough rounders, nailers, sole layers, 






shank nailers, welt beaters, trimmers, welt 






scarfers, welters, tack pullers, lasters, pull- 


Light material 


20 


overs, edge setters, edge trimmers, breasters, 


Dark material 


100 


sluggers, levelers, randers, wheelers, channel 






layers 






Sorting and storage areas 




10 


Aisles 




5 



T r eers /Light material 


20 


IDark material 


100 


Embossing, spraying, cleaning, scourers, buffers, JLight material 


20 


polishers, hand repairers \Dark material 


100 


Benches 


20 


Packing and Shipping Department 




Box making, bench work, shipping room 


10 


Office 


30 


Aisles 


5 



RUBBER SHOES 



Coaters and mill run compounding 10 

Varnishing, vulcanizing, calenders, coating, upper and sole cutting 30 

Sole rolling, lining, cutting, and all making operations 50 

Office 30 

Aisles 5 



10-132 



I E S LIGHTING HANDBOOK 



LIGHT-REFLECTING 
WEDGE OF WOOD COVER 
ED WITH SPECULAR 

SHEET ALUMINUM 




FIG. 10-98. Suggested use of light-reflecting 
wedges for last storage bins. 

Note: It is recommended that walls and 
ceilings of all bins be painted with high reflec- 
tance paint. 



and roof of each bin may be 
painted with a high-reflectance 
paint such as aluminum. 
Light striking these- wedges, at 
the front of the bin, is reflected 
to the walls and ceiling, thus 
increasing the level of illumi- 
nation by about 50 per cent 
in the bin interior. (See Fig. 
10-98.) The polishing effect 
of the sliding leather over the 
wedges maintains the specular 
reflectance of the surface. 

Upper department. An up- 
per department generally is 
divided into the following sections: (1) sorting; (2) trimming, cutting, and 
staying; (3) lining; (4) upper cutting; (5) marking and skiving; and (6) 
assembling. 

When an order is received for a certain grade of shoes, the sorting de- 
partment grades the leather as to color and quality. For this work a 
uniform illumination level of 20 footcandles for light materials and of 100 
footcandles for dark materials is recommended. The sorting department 
generally is located at the north side of the building so that skylight may 
be utilized. 

Skilled workers then split each piece of leather into as many sheets as 
possible and cut out individual parts for uppers. This work generally is 
done on tables 30 to 36 inches above the floor. 

The various pieces go to the counting department where they are counted 
and marked with job numbers. Skiving, which consists of the mechanical 
thinning of edges of the uppers so that they can be turned over to present 
a finished appearance, is the next step. The work of assembling consists 
of bringing together the various parts which make up the uppers such as 
lining, stay, vamp, counter, toe, tip, etc. For these operations a uniform 
illumination level of 20 footcandles for light materials and of 100 footcandles 
for dark materials is recommended. 

Stitching department. In the stitching department the following opera- 
tions are typical: (1) lining; (2) tip; (3) closing and staying; (4) boxing; (5) 
top stitching; (6) buttonholing and stamping; and (7) toe closing. 

These operations present difficult seeing tasks. A uniform general il- 
lumination level of 10 footcandles should be supplemented by local lighting 
on the machines. It is recommended that this lighting be secured by fasten- 
ing to the table, at each machine, near the needle point and on the right- 
hand side of the operator, an adjustable arm carrying an opaque reflector 
and a lamp. For light materials 30 footcandles on the work is recom- 
mended. For dark goods a level of not less than 100 footcandles of illumi- 
nation is recommended. A ratio of supplementary to general levels of 
illumination as great as 10 to 1 usually is permissible. 



INTERIOR LIGHTING 10-133 

Reflected light from the polished working surface of the machine should 
be cast over the right shoulder of the operator, between him and the opera- 
tor on his right. This position also provides a secondary shadow across 
the leather just ahead of the needle point which improves visibility at the 
point of work because of the increased contrast. 

For specialized work in this department such as eyeletting, buttonholing, 
perforating, etc., machines are used which have relatively large overhangs. 
These cause bad shadows when illumination is provided by luminaires 
mounted overhead. It is recommended that a local lighting system be 
used to supplement the uniform general illumination. 

In all cases levels of illumination of not less than 20 footcandles should 
be provided on the work. 

Making department. The making department in the average plant is 
subdivided according to operations as follows: (1) vamping; (2) welt- 
bottoming; (3) bottoming; (4) heeling; (5) turning; and (6) standard, 
screw, nail, or pegged shoe making. 

In some plants this department is called the gang room and occupies an 
entire floor. 

Usually this department is located in the factory area with the highest 
natural illumination level. A general electrical-lighting system also 
should be installed to provide 20 footcandles. Local lighting should be 
used to supplement the natural and electric lighting not only to provide 
at all times the high levels of illumination required at the work, but also 
to mitigate shadows of overhanging machine parts. 

Lasters, sole layers, levelers, and nailing machines may be illuminated 
by diffused light. The source location is not critical. Other machines in 
the making department should be illuminated from the rear and to the 
right of the operator. The vertical as well as horizontal illumination level 
is most important. For recommended levels see Table 10-15. 

Finishing room. In the finishing room shoes are inspected and faults 
are corrected. Treeing machines are used in this area for ironing out 
wrinkles. From here the shoe goes to the final inspection and thence to 
the packers and shippers. A uniform illumination level of 20 footcandles 
is recommended for this work if the materials have a high reflectance, and 
100 footcandles if they have a low reflectance. 

Packing and shipping department. The work in this department com- 
prises matching and numbering shoes, inserting laces, and packing pairs 
in individual boxes on benches. In most plants shelves extend to the 
ceiling. The recommended illumination level is 10 footcandles. 

Rubber-Shoe Manufacturing 

In rubber-shoe manufacturing plants typical operations include the 
following: (1) washing; (2) compounding and milling; (3) cutting and 
calendering; (4) drying; (5) sole rolling and cutting; (6) making; (7) var- 
nishing and vulcanizing; and (8) packing and shipping. 

In the washing department crude rubber is cut up by band saws. A 
uniform general illumination level of 10 footcandles is recommended for 



10-134 I E S LIGHTING HANDBOOK 

washing and cutting and also for the compound and mill area except where 
hoods are placed over the compounding machines. In such cases local 
lighting should be provided by luminaires installed under the hood with a 
reflector directed at the point of work. 

As materials pass over the cutting and calendering machines, care must 
be taken to see that the coating is applied correctly. Calenders, especially 
the three- or four-roller type, should be lighted by luminaires on both sides 
of the machines. The light should be well diffused to avoid sharp shadows 
and glare. 

After cutting or gumming, rolls go to the drying room where they are 
dried by steam heat. Where this department is confined to the center of 
the building and has no direct general ventilation, there is an explosion 
hazard. Where such is the case, explosion-proof or vapor-proof lighting 
units are recommended. Supplementary lighting equipment provides 
light at both front and rear ends of the sole rolling machine. An illumina- 
tion level of 30 footcandles is recommended. 

In the sole and upper cutting department, operators work rapidly with 
sharp knives. A uniform illumination level of at least 30 footcandles 
throughout the area is recommended. Luminaires should be mounted as 
high as possible. In some plants beam dinkers are used. These should be 
lighted in the manner described on page 10-130. 

The making department is the most important in this type of plant. 
All parts are supplied, cut to shape, to bench workers who use cement to 
attach and complete a shoe. In some cases there is a shelf or rack over the 
center of the bench, extending its entire length. The lasts are placed on 
this shelf and if luminaires are placed over this shelf and hung low, the 
shelf causes a sharp shadow on the working areas of the bench. A general 
lighting installation producing not less than 50 footcandles on the work 
is recommended. 

In the varnishing and vulcanizing areas, a uniform illumination level of 
about 30 footcandles is recommended. 

FLUID MILK INDUSTRY 

Recommended minimum footcandle values to be used for guidance in the 
solution of lighting problems in the fluid milk industry are included in 
Table 10-16. 

Loading and Unloading Platforms 

Areas used during dark winter mornings and evenings and at night for 
loading and unloading should be electrically lighted to a uniform minimum 
level of 10 footcandles. This should be supplemented by local lighting 
equipment to increase the level to a minimum of 20 footcandles in the areas 
used by checkers who make a detailed count of kinds and numbers of milk 
bottles being loaded or unloaded. Industrial-type, direct-lighting equip- 
ment is suitable. 



INTERIOR LIGHTING 



10-135 



Table 10-16. Recommended Maintained Minimum Illumination Levels 
for the Fluid Milk Industry 



LOCATION 



Boilers 

Bottle storage 

Bottle sorting 

Bottle washers 

Cap washers 

Cleaning fittings and pipes. 

Cooling equipment 

Filling and inspection 

Gauges 

Laboratories 

Loading platforms 

Meter panels 

Pasteurizers 

Receiving room 

Scales 

Separators 

Storage refrigerator 

Tanks 

Thermometers 

Vats 

Weighing room 



FOOTCANDLES 
MAINTAINED 
IN SERVICE* 


FOOTLAMBERTS 


10 







10 




— 


50 




— 


20 




250f 


20 




200$ 


50 




— 


30 on 


facet 


— 


50 




— 


10 




. — 


30 on 


facet 


— 


20 




— 


20 




— 


30 




— 


20 




— 


10 




— 


■ — 




5 


30 on 


facet 


— 


50f 
10 








* These footcandle values represent order of magnitude rather than exact levels of illumination. 

f See text for explanatory details. 

j Brightness of luminous area toward which the workman sights through pipe. 

Bottle-Storage Rooms 

In bottle-storage rooms it is necessary to pick out foreign articles, remove 
caps, sort out very dirty and foreign bottles, and to sort and segregate 
various types such as retail and store bottles. A minimum illumination 
level of 50 footcandles should be maintained throughout sorting areas. 
A uniform illumination level of 10 footcandles is recommended for the re- 
maining portion of the bottle-storage room. 

Bottle Washers 

One of the most difficult problems in a modern dairy is to light milk 
bottles as they are discharged from a bottle-washing machine so that 
foreign matter, fractures, etc., are quickly and easily seen. 

Method of operation. The complete operating cycle of a typical bottle- 
washing machine lasts 6 seconds. The clean bottles stand still (up-ended) 
for 1^ seconds in full view of the operator, at a distance of 40 inches. Dur- 
ing this time (0.2 second per bottle) he inspects them while picking up a 
load of dirty bottles. If the dirty bottles do not require his attention, he 
may have a fraction of the remaining 4| seconds to inspect some of the 
clean ones as they move out. General illumination of not less than 20 
footcandles should be provided, supplemented with a minimum of 50 foot- 
candles of well-diffused light at the loading end of the washer. 



10-136 



I E S LIGHTING HANDBOOK 




*.'■# 




FIG. 10-99. Closeup of bottles lighted by luminous inspection panel. Bottles 
may be inspected efficiently for foreign matter, and fractures are made easy to see. 

Inspection. Bottles are inspected both while being placed in the washer 
and after discharge from the washer. The purpose of the inspection is to 
discard foreign or store bottles; bottles stained beyond recovery; bottles 
with chipped necks or cracks; and incompletely washed bottles. Foreign 
bodies such as paper caps, wire, and nails must be removed. 

It was found experimentally that inspection of bottles silhouetted against 
a low-brightness luminous surface as in Fig. 10-99 is the most efficient 
method. A luminous inspection panel may be incorporated in the un- 
loading mechanism in the form 
of an inspection light-box. A 
typical box consists of a sheet- 
metal enclosure containing 
lamps and auxiliary equip- 
ment, the open front of which 
is covered with a translucent 
plastic sheet. The assembly 
is placed in the unloading 
mechanism in such a way that 
when the bottles are pushed 
out of the washer they are sil- 
houetted against the luminous 
panel. Incomplete washing, 
cracks, chips, foreign matter 
in the bottles, etc., can be 
detected readily. (See also 
Fig. 10-100.) 
A maximum brightness of 500 footlamberts is permissible with 250 foot- 
lamberts the preferred value. 




FIG. 10-100. Illumination of bottle washers 
which cannot be modified to accommodate a 
luminous panel may be improved by installing 
a large-area luminaire directly above the in- 
spection end. 



INTERIOR LIGHTING 10-137 

Manufacturing Areas 

General lighting equipment in a fluid milk plant should provide an il- 
lumination level of at least 20 footcandles. The light should be well 
diffused. Rooms should be finished with ceiling reflectance of 75 per cent 
or more and with side-wall reflectance of from 50 to 60 per cent. 

The lighting should be such that there will be no specular images of the 
light sources formed on the surface of a bottle, whether empty or full, that 
will interfere with the proper inspection of the bottle or the finished product. 
The distribution characteristics and spacing of luminaires should be such 
that no sharp shadows will be cast. Areas adjacent to walls or corners 
should not fall below an illumination level of at least 10 footcandles. 

REFERENCES 

To supplement the condensed Handbook treatment, the Recommended Practices of the Illuminating 
Engineering Society listed on page 10-28 and many papers in the Transactions of the Illuminating Engineering 
Society (through 1939) and in Illuminating Engineering (1940 and later) including the following taken prima- 
rily from those appearing between 1937 and 1947, will be found helpful. Details of outstanding lighting in- 
stallations in various fields will be found in current I.E.S. Lighting Data Sheets. 

Light and Architecture 

1. Lyon, J. A. M., "Luminous Surfaces for Architectural Lighting," July, 1937. 

2. Maitland, VV., "Light and Architecture in England," September, 1937. 

3. Hibben S. G., "How New York World's Fair Exhibitors Use Light," September, 1939. 

4. Beggs, E. W., and Woodside, C. S., "Techni'a 1 Aspects of Architectural Lighting," December, 1931. 

5. McCandless, S. R., "An Outline of a Course in Lightin g for Architects," May, 1931 . 

6. Potter, W. M., and Meaker, P., "Luminous Architectural Elements," December, 1931. 

7. Vaughan, M. S., "The Influence of Architecture and Decoration on Residence Lighting," November, 
1937. 

8. Schweizer, A C, "Light as Decoration and as an Art," May, 1939. 

9. Rolfe, W. T., "An Architect Looks at Illumination," April, 1940. 

10. Irvin, R. W., "The Relation of Lighting to Interior Design," June, 1940. 

11. Woodside, C. S., "Cove Lighting Design." March, 1936. 

12. Owings, N. A., "The Illuminating Engineer and the Architect," June, 1942. 

Maintenance 

13. Beggs, E. W.j "Planning for Maintenance," December, 1941. 

14. Gaetjens, A. K., "Lighting Maintenance in War Industry Plants," luly, 1942. 

15. Davis, \V., "Solving Lighting Maintenance Problems in Aircraft Plants," April, 1945. 

16. Gaetjens, A. K., "A Guide to Realistic Maintenance Factors for Lighting Installations," May, 1945 

Light and Air-Conditioning 

17. Cook, H. A., "Lighting the Detroit Edison Company Service Building," December, 1939. 

18. Committee Report, "Lighting and Air-Conditioning Design Factors," September, 1941. 

19. Lewis, S. R., "Lighting, Air-Conditioning and Air Cleaning," January, 1945. 

Residence and Farm 

20. Commery, E. W., "Modern Lighting in a Modern House," November, 1937. 

21. Bailey, J. T., "Some Practical Aspects of Lighting Kitchen Work Areas," September, 1938. 

22. Sharp, H. M , "Light as an Ally of the Safety Engineer," June, 1939. 

23. Fahsbender, M., "Practical Aspects of Farm Home Lighting," July, 1939. 

24. Recommended Practice in the Construction and Illumination Performance of Residential Luminaires, 
July, 1939. 

25. Randall, W. C, and Martin, A. J., "Daylighting in the Home," March, 1931. 

26. Fahsbender, M., and Slauer, R. G., "Fluorescent Lamp Applications in the Home," September, 1940. 

27. Little, W. F., "Progress in Rating Residence Luminaires," December, 1940 

28. Commery, E. W., McKinlay, H.G.,and Webber, M.E. /'Residence Blackout Methods and Materials," 
September, 1942. 

29. "Recommended Practice of Home Lighting," June, 1945. 

30. "Dairy Farm Lighting," Lighting News, September, 1938. 

Office Lighting 

31. Johnston, H. L., "Daylight Variations," July, 1939. 

32. Vinther, P. N., "Lighting Mercantile Bank Building," November, 1944. 

33. "Recommended Practice of Office Lighting," September, 1942. 

34. Committee Report, "Lighting Application in the Southwest," July, 1944. 

35. "Precast Coffers Light Shop Office," November, 1944. 

36. Larson, A. W., and Kahler, W. H., "An Improved Technique in Small Office Lighting," September, 
1945. 



10-138 I E S LIGHTING HANDBOOK 

Store Lighting 

37. Stair, J. L., Foulks, W. V. C, "What's New in Store Lighting," January, 1938. 

38. Wolff, F. M., "A New Trend in Window Display Lighting," January, 1938. 

39. Harrison, W., and Spaulding, H. T., "Overcoming Daylight Reflections in Show Windows," Decem- 
ber, 1922. 

40. Alexander, H. M., "Practical Aspects of Luminous Storefronts," March, 1939. 

41. Gilleard, G., "Illumination Designed for Buying in Self-Service Food Stores," June, 1940. 

42. "New Model Store at Chicago Lighting Institute," Lighting News, July, 1940. 

43. Wolff, F. M., "The Illumination of Jewelry and Tableware," May, 1941. 

44. Stair, J. L., and Foulks, W., "New Technique in Display Lighting," March, 1942. 

45. Allison, R. C, "Merchandising with Light," September, 1944. 

46. "Worcester Chain Store Lighting Attractive," November, 1944. 

47. "Dress Shop Utilizes Combination Lighting," November, 1944. 

48. Owings, N. A., "Comments on Lighting Layout and Design," December, 1944. 

49. Chapin, R. J., "Post War Requirements of Department Store Lighting," December, 1944. 

50. Welch, K. C, "Economics of Store Lighting," December, 1944. 

51. Sturrock, W., and Shute, J. M., "Effect of Light on the Drawing Power of the Show Window," Decem- 
ber, 1922. 

52. "New 40-watt Reflector Showcase Lamp Announced," Lighting News, July, 1939. 

School Lighting 

53. Albert, F. C, "Scholarship Improved by Light," December, 1933. 

54. Dearborn, R. L., "A Study of Brightness, Distribution and Control of Classroom Lighting," September, 
1937. 

55. Brown, L. H., "The Control of Natural Light in Classrooms," June, 1939. 

56. Caverly, D. P., "An Analysis of Photoelectric Classroom Lighting Control," September, 1939. 

57. "Recommendations for Classroom Lighting," Lighting News, June, 1940. 

58. Brown, L. H., "The Design of Classrooms for High Level Daylight Illumination," March, 1941. 

59. Luckiesh, M., and Moss, F. K., "Effects of Classroom Lighting upon Educational Progress and Visual 
Welfare of School Children," December, 1940. 

60. Slauer, R. G., "Brightness Limits of Wisconsin School Lighting Code," January, 1945. 

61. Harmon, D. 6., "Lighting and Child Development," April, 1945. 

62. Biesele, R. L., Jr., Folsom, W. E., and Graham, V. J., "Control of Natural Light in Classrooms," Sep- 
tember, 1945. 

Commercial and Public Buildings 

63. Miehls, G. H., "Building for War Production," December, 1942. 

64. Moodie, E. W., "Lighting for National Defense Buildings and Services," June, 1943. 

65. Conway, C. B., "Relighting the Walters Art Gallery," February, 1938. 

66. Logan, H. L., "Modeling with Light," February, 1941. 

67. Steinhardt, L. R., "The Illumination of Statuary," April, 1941. 

Industrial Lighting 

68. "Report on Lighting in the Shoe Manufacturing Industry," March, 1937. 

69. "Report on Lighting in the Candy Manufacturing Industry," May, 1937. 

70. "Report on Lighting in the Textile Industry, Grey Goods and Denim," March, 1937. 

71. "Progress Report on Lighting in the Printing Industry," March, 1936. 

72. "Researches on Industrial Lighting — Lighting for Silk and Rayon Throwing and Wide Goods Weav- 
ing," January, 1938. 

73. "Studies in Lighting of Intricate Production, Assembly and Inspection Prooesses," December, 1937. 

74. Sharp, H. M.,and Crouch, C. L., "The Influence of General Lighting on Machine Shop Tasks," March, 
1939. 

75. "Lighting for the Machining of Small Metal Parts," January, 1939. 

76. "Lighting of Power Presses," February, 1939. 

77. Ross, M. W., "Lighting for the Cleaning and Pressing Industry," June, 1937. 

78. Sharp, H. M., "Light as an Ally of the Safety Engineer," June, 1939. 

79. Diggs, D. M., "External Plant Lighting for Safety," April, 1940. 

80. Smith, J. M., "Relighting a Large Industry," September, 1940. 

81. Austin, W. J., "Operating Advantages of Controlled Conditions Plants," January, 1941. 

82. Caverly, D. P., "Improved Illumination for Textile Operations with Fluorescent Lamps," April, 
1941. 

83. Tuck, D. H., "Protective Lighting for American Industry," July, 1941. 

84. "Report on Lighting in the Fluid Milk Division of the Dairy Industry," November, 1942. 

85. Dates, H. B., "Remarks Concerning Wartime Industrial Lighting in Connection with Conference 
Presentation of Report of the Committee on Light in Wartime," December, 1942. 

86. "Value of Good Lighting in War Production, A survey of Opinion from a Cross-Section of American 
Industry," January, 1943. 

87. Wittekind, J. R., "Industrial Vision," February, 1943. 

88. Kohler, W., "Good Light— A Social Necessity," March, 1943. 

89. Prideaux, C. F., "Engineering Twenty- Four Hour 'Daylight' to Master Manpower Problems," May," 
1943. 

90. Fowler, E. W., "Lighting a Color Register Room," May, 1944. 

91. Attaway, W. N., "Management Comments on Good Plant Lighting," July, 1944. 

92. Trauernicht, H., and Kuenemann, W. A., "Swinging Fixture Mounting Designed for Large Lathe," 
July, 1944. 

93. "Practical Solutions of Lighting Problems," September, 1944. 

94. Darley, W. G., and Gaetjens, A. K., "What Price Industrial Eye Comfort?" December, 1944. 

95. Tiffin, J., "Vision and Industrial Production, April, 1945. 

96. Feinberg, R., "Illumination and Vision Conservation in Industry," May, 1945. 

97. Wright, L. D., "Australian Experience of Nation-wide AppUcation of Industrial Lighting Standards," 
September, 1945. 

98. Caverly, D. P., "Essential War Metals Saved by the Lighting Industry," March, 1943. 

99. Nelson, J. H., "Lighting a Small Commutator," January, 1944. 



SECTION 11 
EXTERIOR LIGHTING 

Exterior-lighting applications discussed in this section are various types 
of electrical advertising and decoration, including signs, luminous com- 
mercial fronts, and floodlighting. Lighting for gardens, pools, fountains 
and waterfalls and for the prevention of sabotage, theft, and accident also 
is discussed. 

Illumination for outdoor sports is covered in Section 12, and Section 13 
describes current lighting practice for transportation areas, including streets 
and highways, railroads, and airports. 

LIGHTING FOR ADVERTISING 

Electrical advertising in the United States dates from the latter part of 
the nineteenth century and since that time has become one of the strong 
mediums of the art. It is used for several purposes, including: 
Identifying a place of business 
Advertising a building or plant 
Advertising a product or a service 

Electrical advertising differs in several respects from other major classes 
of advertising such as printed matter and radio. In the case of printed 
matter (newspaper, magazine, and direct-mail advertising), the reader 
handles the copy which attracts his attention. No time limit is imposed on 
the reader's perusal, and printed characters are planned to contrast well 
with their background. Radio advertising appeals to a listener through 
his hearing sense, after attracting his attention. 

Electrical-sign advertising, on the other hand, to be successful in terms 
of present-day business economics, should gain the observer's attention 
and serve its purpose in the relatively short period of a few seconds. 

ELECTRIC-SIGN CHARACTERISTICS 

Outdoor electric signs may be classified as follows: 

1. Exposed incandescent lamp signs. 

2. Enclosed lamp signs. 

3. Silhouette signs. 

4. Electric-discharge lamp signs. 

5. Combination signs (incandescent and discharge lamps). 

6. Poster panels, panel signs, and wall signs. 

They may be evaluated from two interrelated approaches: legibility and 
advertising effectiveness. 

Size. Physical location, desired legibility range, and character bright- 
ness determine the minimum letter height required for legibilty. However, 
to attain advertising effectiveness, letter heights of twice minimum height 
generally are employed for legibility. Vertical columns of letters, though 
usually an aid in increasing the apparent size of a sign, are more difficult 
to read than horizontal columns. 



Note: References are listed at the end of each section 



11-2 



I E S LIGHTING HANDBOOK 



Brightness. Letter brightness and contrast between letter and back- 
ground are factors influencing the legibility of a letter and the rapidity 
with which it is recognized. Contrast between the average sign brightness 
and that of its background determines, in a large measure, the manner in 
which the sign stands out. Brightness and contrast attract attention. 

Location and position. The advertising value of a sign depends on the 
greatest possible number of persons seeing it. This is a function of its 
location. 

Distinctiveness. One of the elements of a good electric sign is that it 
possess distinctiveness and individuality. It should create a pleasing, 
favorable impression, should have public appeal, and should be remembered 
easily. 

Motion. Motion increases the attracting power and memory value of a 
sign. It capitalizes on the instinctive trait of people to be aware of and to 
give heed to moving things. 

Color. Often color is incorporated in a sign because (1) it provides 
contrast and therefore is an important factor in legibility, (2) it may aid in 
attracting attention, and (3) it may add distinctiveness. 

Exposed Incandescent Lamp Signs 

These signs are constructed so that the lamps are exposed to direct view. 
This type is well suited for application where long viewing distances are 
involved. Motion and color can be incorporated very easily in such 
signs. An outstanding example of the exposed lamp sign is shown in Fig. 
11-1. 




FIG. 11-1. This spectacular exposed lamp sign in Times Square, New York City, 
is over a city block long. Approximately 30,000 lamps are flashed in sequence to 
suggest motion of the figures in the display. 



EXTERIOR LIGHTING 



11-3 




Channels (Fig. 11-2) used on 
exposed lamp signs comprise a 
background on which a succes- 
sion of lamp sockets are fastened 
between sides which outline a 
letter. The sides prevent lamps 
from illuminating the adjacent 
area. Thus the}*- help to main- 
tain contrast between letter and 
background. Also, they pre- 
vent one portion of the sign 
from interfering with the legi- 
bility of another portion, out- 
,.,,,,, ? , FIG. 11-2. Letter channels carry lamp 

line the letters for improved , , , , .... ., •„ , ,. ,, 

r sockets and by restricting the spilled light 

daytime legibility, and increase f rom the background increase contrast be- 
brightness uniformity. tween letter and background. 

Effective range. The range of advertising effectiveness of exposed lamp 
signs is from 250 feet to several miles. 

Legibility. Legibility is primarily a function of letter size and form or 
design, lamp spacing and brightness, and contrast between letter or design 
and background. 

Block letters possess greater legibility than do ornamental styles, script, 
and special forms, although the latter types may be used to gain distinctive- 
ness. Wide, extended letters are more legible than tall, thin letters. 

Letter size. The minimum letter height employed on an exposed lamp 
sign usually is greater than the height necessary to gain recognition. For 
purposes of advertising and quick reading, it is common practice to provide 
exposed lamp signs with letter heights that are at least twice those neces- 
sary for recognition. 

For simple block letters (the width equal to three-fifths of the height) 
the minimum letter height for advertising and quick reading purposes is 
given by the formula: 

tt _. R where H a = vertical height of letter, for adver- 
" ~ 250 tising and quick reading, from top 

lamp to bottom lamp (feet) 
R = maximum range of sign for adver- 
tising effectiveness (feet) 
Smaller letters will have less advertising value, but they will be legible 
to most people if their height is not much less than that given by the 
formula: TT D where H r — minimum vertical height of letter 

500 for recognition from top lamp to 

bottom lamp (feet) 
D = maximum distance at which letter is 
recognized by majority of people 
(feet) 



H r 



11-4 



I E S LIGHTING HANDBOOK 



O- 

o- 
o 
o 
o 
o 
o o o o 



" LAMP 
.SPACING 



LETTER 
STROKE 



■oooo 

o 

o 



oo o 

o 

o 



oooo 



v -_- 



LETTER 
SPACING 



FIG. 11-3. Important dimensions 
in the design of exposed lamp letters. 



S = 



Letter width, height, stroke, and 
spacing, and lamp spacing are illus- 
trated in Fig. 11-3. (See Table 11-1, 
also.) 

Lamp spacing. The proper spacing 
between lamps that comprise a letter 
is determined by the minimum viewing 
distance. 

Spacing may be calculated by the 
following formula: 

MVP 
1,000 



where 



s = spacing between centerlines of lamps 
(feet) 
MVD = minimum viewing distance (feet) 
Lamp wattage rating. The incandescent lamp wattage employed depends 
upon the general brightness of surroundings, and background, as the sign 
is viewed. Consequently, a roof sign, even if located in a brightly lighted 
area in the business center of a city, might at night always be viewed 
against a dark sky. Such a sign would require the same lamps called for in 
an outlying dark district. 

Table 11-2 indicates the proper spacing and wattage of clear lamps for 
exposed lamp signs located in different areas classified according to the 
probable brightness of a sign's background. 



Table 11-1. Dimensions of Exposed Lamp Letters for Equal 
Advertising Effectiveness at Different Ranges 



EFFECTIVE 
RANGE (feet) 


MAXIMUM 

DISTANCE 

LEGIBLE 

(feet) 


DIMENSIONS (inch 


es) 


LETTER 
SPACING 


Height 


Width 


Stroke 


(inches) 


200 


400 


10 


6 


2.5 


4 


250 


500 


12 


7 


2.5 


4.75 


300 


600 


14 


8 


2.5 


5.5 


350 


700 


17 


9.5 


2.75 


6.5 


400 


800 


19 


11 


3 


7.5 


450 


900 


21.5 


12.5 


3.5 


8.5 


500 


1,000 


24 


14 


4 


9.5 


750 


1,500 


36 


26 


5 


14.5 


1,000 


2,000 


48 


29 


6 


19 


1,500 


3,000 


72 


43 


9 


20 


2,000 


4,000 


96 


58 


12 


38 


2,500 


5,000 


120 


72 


15 


48 


3,000 


6,000 


144 


86 


18 


58 


3,500 


7,000 


168 


100 


21 


68 


4,000 


8,000 


192 


115 


24 


77 


4,500 


9,000 


216 


130 


28 


87 


5,000 


10,000 


240 


144 


30 


96 



EXTERIOR LIGHTING 



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11-6 



I E S LIGHTING HANDBOOK 



If incandescent lamps with colored glass bulbs or clear bulbs with colored 
accessories are employed, lower letter brightness will result than when equal 
wattage lamps with clear bulbs are used alone. 

For equal advertising effectiveness colored surfaces require less brightness 
than neutral surfaces as shown in Table 11-3. 



Table 11-3. Relative Wattage of Colored and White or Inside Frosted 

Incandescent Lamps Required to Give Signs of Various Colors 

Approximately Equal Advertising Value 



COLORED 




WHITE OR INSIDE FROSTED LAMP RATING (watts) 




LAMP 








RATING* 

(watts) 


Daylight 
Bluet 


Yellowf 


Amber- 
Orangef 


Green f 


Redf 


Bluet 


10 


15 


10 


10 


25 


25 


50 


15 


15 


10 


10 


25 


25 


50 


25 


25 


25 


25 


50 


50 


50 


40 


50 


50 


50 


50 


60 


60 


60 


eo 


60 


60 


100 


100 


150 


100 


100 


100 


100 


150 


150 


200 



* Color similar to that of sign surface; 100-watt or larger lamps require color hoods, 
t Color of sign surface and lamp to which white or inside frost rating compares. 



Lamp types. For exposed lamp signs located where rain or snow could 
fall on relatively hot glass, vacuum-type incandescent lamps are recom- 
mended. They are available in 6-, 10-, 25-, and 40-watt ratings in both 
clear and colored bulbs, and in 25- and 50 -watt ratings in daylight bulbs. 
Inside-coated or colored-bulb lamps are recommended in exposed lamp 
signs, since their color is more stable than that of outside coated lamps. 

Reflector signs. Efficient reflectors can be employed to direct light to 
areas in which it is most useful and create letter brightnesses several times 
that of a corresponding letter without reflectors. 

Typical polished reflector equipment is shown in Fig. ll-4a and a com- 
plete letter using such equipment is shown in Fig. ll-4b. The reflecting 
device consists of a small polished reflector with a medium-screw base that 
will fit into standard sockets. This reflector uses a 3-, 6-, or 7-watt, cande- 
labra- or a 6- or 10-watt, intermediate-base lamp. Either clear or colored 
glass roundels in prismatic designs are placed over the reflector opening. 
Where excellent side-angle brightness is a requirement, cover glasses should 
be employed. For equal advertising value over a limited area in certain 
directions, polished reflectors, if used, may result in a rebuction in required 
wattage as great as 75 per cent. 

Enclosed Lamp and Silhouette Signs 

Enclosed lamp signs employ light sources enclosed with glass, plastic, or 
other light-transmitting materials. The letters or designs usually are 
opaque but may be etched in light-transmitting material. 



EXTERIOR LIGHTING 



11-7 




FIG. 11-4. a. Typical polished reflectors and cover glasses for 
sign lamps, b. Sign letter with polished reflectors and cover 
glasses installed, c. Parabolic reflectors such as these appear as 
a continuous line of light when the lamps are operating, d. When 
operated in a specular trough reflector such as this, a single row 
of lamps appears as three rows. e. A specular reflector of cor- 
rugated cross section forms many source images and spreads them 
in a broad pattern over its surface. 



11-* 



I E S LIGHTING HANDBOOK 



Silhouette signs are those in which opaque letters, designs, etc., are lo- 
cated in front of a luminous background and appear in silhouette against 
it. Figure 11-5 shows typical silhouette signs. 






FIG. 11-5. Typical silhouette sign construction. 

Effective range. Enclosed lamp and silhouette signs do not have as great 
effective range as similar exposed lamp signs because contrast between 
letters or designs and background is reduced by loss of brightness in the 
enclosures. 

The maximum range of effectiveness for advertising purposes of enclosed 
lamp and silhouette signs is approximately 1,000 feet. 

Etched letters. The sign characters are etched on the light-transmiting 
medium which may be translucent marble, ceramic glass, plastic, etc. 

Painted letters. Letters are painted on the light-transmitting medium. 
This type is economical from the standpoint of first cost. Peeling with age 
may be a maintenance difficulty. 

Metal letters. Many styles of cast metal letters are available. This 
type may be changed quickly and easily. 

Block letters. The block type of letter is used 
commonly where side-angle effectiveness is im- 
portant. (See Fig. 11-6.) 

Translucent letters. With colored light sources 
behind it, this type of letter makes possible 
changes in color. 

Bi-planc letters. This type is constructed of 
two simple channeled letters, one in front of the 

5 other. Behind each letter, light sources illumi- 

II 1 nate its background. (See Fig. 11-5.) 

I I | n Legibility. In general, block letters are recog- 

I &J I * nized as being more effective than flat, thin 

I letters or script, although use of the latter types 

should not be precluded as they may aid in 
the achievement of individualit}'. Wide ex- 
FIG. 11-6. Effect of letter tended letters are more legible than narrow, 
design on legibility at an angle, condensed ones. 




EXTERIOR LIGHTING 



11-9 



Letter size. Letter legibility is a function of the ratio of stroke width to 
letter height. Figure 11-7 shows this relationship for any given letter 
height. The most favorable proportion is 0.15. This does not mean that 
other proportions should be disregarded. Individuality and distinctiveness 
are achieved through the use of other proportions. Also, the desired viewing 
distance for many signs is much less than the maximum legibility distance 
for the patterns employed. 



ul O 
Q P 

5 z 

D O 
- U 

X LU 

< DC 

5 

























































'w= 

* 


0.125 

! 


N. 


W=l.5 IN. 

r-4 




w 


=3 INA 

i ,1 


F 




E* 

+ 1 







4 8 12 16 20 24 28 32 36 

WIDTH OF LETTER STROKE IN PER CENT 

OF LETTER HEIGHT 

FIG. 11-7. Effect of stroke on easy rec- 
ognition distance of an opaque block letter on 
a luminous background. Test object (10 inch 
x 7 inch letter E) was viewed against a 72 
inch x 35 inch luminous panel erected on a 
dark street. Scattered lights were visible in 
the field of view, also. 



For block letters of a width equal to three-fifths of the height and a ratio 
of stroke to height of 0.15, the minimum letter height is given by the 
formula : 



H a = 



440 



where 



H a = minimum letter height for advertis- 
ing and quick reading (feet) 
R = maximum range of advertising ef- 
fectiveness of sign (feet) 
Smaller letters will have less advertising value, but will be recognized 
readily if their heights are not less than the values determined by the 
formula : 



where 



H T = 



II 



D_ 

660 



vertical stroke height of letter for 
ready recognition (feet) 
D = maximum distance at which letter 
is readily recognized (feet) 



11-10 



I E S LIGHTING HANDBOOK 



For ratios other than 0.15, the maximum distance, D, for ready rec- 
ognition, is shown in Fig. 11-8. 




12 16 20 24 28 32 

HEIGHT OF LETTERS IN INCHES 

FIG. 11-8. Effect of height on easy recognition distance of an 
opaque block letter on a luminous background for various stroke 
per height ratios. The test object (10 inch x 7 inch letter E) was 
viewed against a 72 inch x 35 inch panel with brightness of 120 
footlamberts under the same conditions as in Fig. 11-7. To obtain 
distance values for other panel brightnesses, multiply the value 
from this graph corresponding to the proper letter size by the 
distance factor obtained from Fig. 11-9. 

Brightness and size of illuminated background also affect the maximum 
distance at which a sign is effective and readily recognizable. Curves 
showing the effect of luminous area on distance for ready recognition are 
given in Fig. 11-9. In determining luminous area, deductions should be 
made for the area obstructed by the letters. 

FIG. 11 9. Effect of a 
partially obscured lumi- 
nous background area on 
easy recognition distance 
for an opaque block letter 
viewed against it. Unity 
on the relative distance 
scale corresponds to 552 
feet for a test object (10 
inch high letter E, 1.5 
inch stroke) viewed 
against a panel of the 
same size and brightness 

o as in Fig. 11-8. To ob- 

net luminous area in square feet (unobscured) tain maximum ready rec- 
ognition distance for a letter of another size, obtain the value for a letter of that size 
from Fig. 11-8 and multiply that value by the distance factor. 




EXTERIOR LIGHTING 



11-11 



Sign brightness. For equal advertising effect, the luminous element 
brightness of an enclosed lamp sign will vary with the brightness of the 
surroundings that form its background. Recommended brightnesses for a 
variety of signs and other objects are given in Table 11-4 for low-, medium-, 
and high-brightness backgrounds. 

Table 11-4. Recommended Brightness for 
Exterior Luminous Signs and Elements* 





RECOMMENDED BRIGHTNESS (footlamberts) 


EXTERIOR ELEMENT 


Average Brightness of District 




Low 


Medium 


High 


Luminous-background signs 
Luminous-letter sign 
Flush elements: 

Fascia signs 

Panels 

Parapets 

Recesses 
Principle units in design 
Subordinate elements in design 
Spandrels 
Projecting elements: 

Pylons 
Free-standing columns 

Dominant 

Subordinate 
Marquee and entrance (soffits, 

marquee fascias, luminous 

beams) 
Small luminous facades 


90 to 150 
150 to 200 

30 to 100 
30 to 100 
30 to 100 
30 to 100 
30 to 100 
10 to 50 
10 to 50 

30 to 100 
30 to 100 
30 to 100 
30 to 60 
80 to 150 

80 to 120 


120 to 200 
200 to 400 

50 to 150 

50 to 150 
50 to 150 
50 to 150 
50 to 150 
35 to 80 
35 to 80 

70 to 150 
70 to 150 
70 to 150 
40 to 80 
100 to 250 

100 to 150 


150 to 350 
300 to 600 

100 to 300 
100 to 300 
100 to 300 
100 to 300 
100 to 300 
50 to 150 
50 to 150 

100 to 300 

100 to 300 

100 to 300 

50 to 150 

200 to 400 

120 to 200 



* These values do not apply for colored light, 
mended. 



Wedge Signs 

A wedge sign is a double- 
faced, stick-out type of sign, 
as indicated in Fig. 11-10. 
With lamps placed in a par- 
abolic trough reflector at the 
wall side of the wedge, 
acceptable brightness uni- 
formity of the translucent 
side panels results when 
panels are sloped at an angle 
of approximately 18 de- 
grees. 



Where colored light is employed, field tests are recom- 




FIG. 11-10. Wedge sign with one face re- 
moved to show lamps and reflector. 



11-12 



I E S LIGHTING HANDBOOK 




FIG. 11-11. Typical 
fascia sign construction 
showing important de- 
sign dimensions. 



Fascia Signs 

A fascia sign comprises a reflecting cavity in 
which light sources are placed behind an exposed 
facing of translucent material. Figure 11-11 
shows a schematic diagram of typical fascia signs 
with the more important dimensions noted for 
design purposes. 

In general, the maximum desirable ratio of width 
(per row of lamps) to depth of cavity is 1.5. 
Greater ratios tend to decrease the efficiency of 
the sign element and do not permit maximum de- 
sirable lamp spacing. 

Any cavity with sharp rectangular corners traps 
light; hence, its use is to be discouraged. 

Cavities should be finished with a durable, high- 
reflectance surface. In case the reflecting back- 
ground is subjected to wearing by the elements, 
porcelain-enameled metal or the equivalent is recommended because of its 
permanence and mat finish. Glossy finishes reflect images of the lamps 
which tend to interfere with legibility. 

For uniform panel brightness in the case of opal glass or translucent 

materia] with equivalent 
diffusion characteristics, 
lamps should be spaced 
on centers not in excess 
of 1| times the light cen- 
ter distance behind the 
translucent material. 

Figure 11-12 indicates 
the maximum permissible 
spacing between lamp 
centers to produce accept- 
able panel brightness uni- 
formity for several types 
of diffusing glass. 

The average brightness 
of the district in which a 

2 4 6 8 10 12 14 16 18 fflSoia siffn is loPfltPf] 111- 

S, SPACING IN INCHES BETWEEN LAMP CENTERS IHfeWH. blgU lb iULdieu 111 

wto 11 10 n« i • 1. , 1 fluences the sign bright- 

tl(j. 11-12. Hittect 01 spacing between lamp -p , , 

centers on the minimum distance between lamp and nesS - Kecommended 

panel which will produce acceptable brightness uni- brightness values are 

formity, for several panel materials. given in Table 11-4. 




EXTERIOR LIGHTING 



11-13 



Table 11-5 gives the average brightness of opal glass panels covering one, 
two, and three rows of incandescent lamps, respectively, for different lamp 
wattages and for various relationships of cavity size and lamp spacings. 

Table 11-5. Brightness Data for Fascia Signs or Panels 













AVERAGE BRIGHTNESS DESIRED (footlamber 


ts) 


DIMTW-'.!' >- ' fu,rh,.o 
















50 


100 


150 


200 


300 


400 


W 


X 


D 


S 




Wattage Rating of Incandescent Lamps Requirec 
(one row) 




4 


4 


2.5 


4 








6 


6 


10 


10 


6 


6 


4 


6 


— 


6-10 


10 


15 


15 


25 


9 


8 


6 


9 


10 


15 


25 


25 


40 


40 


12 


10 


8 


12 


15 


25 


25-40 


40 


50 


60 


18 


15 


12 


18 


25 


40 


60 


75 


100 


150 


24 


19 


16 


24 


40 


60 


100 


100 


150 


200 


30 


23 


20 


30 


60 


100 


150 


150 


200 


300 


36 


28 


24 


36 


75 


150 


200 


200 


300 


300-500 


48 


37 


32 


48 


100 


200 


300 


300 


500 


750 






Wattage Rating of Incandescent Lamps Required 






8 


6 


9 




(two rows) 




18 


10 


15 


15-25 


25 


40 


40-50 


24 


11 


8 


12 


15 


25 


25-40 


40 


50-60 


60-75 


30 


13 


10 


15 


15-25 


40 


40-50 


60 


75 


100 


36 


15 


12 


18 


25 


40-50 


60 


75 


100 


100-150 


48 


20 


16 


24 


40 


60-75 


100 


100 


150-200 


200 


60 


25 


20 


30 


50-60 


100 


150 


150-200 


200-300 


300 


72 


30 


24 


36 


75 


150 


200 


200 


300 


300-500 


84 


35 


28 


42 


100 


150 


200 


300 


500 


500 


96 


40 


32 


48 


100 


200 


300 


300-500 


500 


750 






Wattage Rating of Incandescent Lamps Required 






11 


8 


10 




(three rows) 




30 


10 


15 


25 


25-40 


40 


50 


36 


13 


10 


12 


15 


25 


25-40 


40 


50-60 


60-75 


42 


15 


11 


14 


15 


25-40 


40 


50 


60-75 


75 


48 


18 


13 


16 


25 


40 


50 


60 


75 


100 


60 


21 


16 


20 


25-40 


50 


60-75 


75 


100 


150 


72 


24 


19 


24 


40 


60-75 


100 


100-150 


150 


200 


84 


29 


23 


29 


60 


100 


100-150 


150 


200 


300 


90 


32 


26 


32 


60 


100 


150 


200 


200-300 


300 



•See Fig. 11-11. 



Illuminated Block Letter Signs 

Illuminated block letters are suitable for use at low mounting heights. 
Each letter of this type of sign is an indivilual closed lamp sign for which 
data is given on Page 11-6. 



11-14 



I E S LIGHTING HANDBOOK 



Electric Discharge Lamp Signs 

An electric discharge lamp sign usually is an exposed lamp type of sign 
since, in practically all cases, such signs utilize unshielded tubing. Tube 
signs are constructed of gas- filled glass tubing which, when subjected to 
high voltage, becomes luminescent in a color characteristic of the particular 
gas used or of the fluorescent phosphors coated on its inner wall. 

Fluorescent tubing may be made to emit almost any desired color by 
mixing different phosphors. Most colors have a higher lumen output-per- 
watt rating than the gaseous tubing without a fluorescent coating. 

Color. Color produced by any one of these gases may be modified by 
using colored glass tubing, which will transmit only certain colors. 

Gases employed. Table 11-G lists some of the gases which may be used 
and the color of light produced by each. 

A typical tube sign and its wiring are shown in Fig. 11-13. 




FIG. 11-13. Typical tube sign wiring. 

Effective range. The range of effectiveness for advertising purposes of 
tube signs is approximately the same as that of exposed lamp signs of the 
same size, color, and brightness: 250 feet to several miles. 

Legibility. For block letters of a width equal to three-fifths of their 
height, the minimum letter height that will be legible to most people at 
given distances is stated in Table 11-7, for red tubing. When colors other 
than red are employed, distances given in Table 11-7 should be reduced. 
The necessary reduction in the case of blue tubing is 25 per cent; in the case 
of green tubing, it is 35 per cent. 

For a given letter height, the corresponding letter and stroke width may 
be determined from those proportions given in Table 11-1, page 11-4. 

Tubing sizes. Standard sizes of tubing for signs range from 9 to 15 
millimeters, outside diameter, but larger tubing is available. 

Transformers. Several forms of high-leakage-reactance type trans- 
formers are manufactured to supply the high voltage necessary to start 
and operate sign tubing. This voltage is of the order of 5,000 to 15,000 
volts. After a tube sign is lighted, one-third to one-half of the starting 
voltage is necessary to keep it operating. The usual range of operating 
current for tube signs is between 10 and